Pipe fitting elements of the above described type are known, which find application in the connection or union of pipes, lines, devices or components of hydraulic or pneumatic systems. Particularly, these

well-known pipe fitting elements find application in plastic pipe connection for irrigation systems or the like.

In these known pipe fitting elements, the mutually facing clamping surfaces provided on the outer surface of the sleeve and on the inner surface of the ring nut generally have each an annular step. This step typically consists of an annular cylindrical narrowing of the outside diameter of the sleeve, usually situated immediately upstream, with respect to the tightening direction, of a pipe lead-in section at the sleeve end turned towards the pipe to be connected, and of a corresponding widening of the inside diameter of the ring nut end turned towards the pipe. During the clamping operation, after inserting the sleeve into the pipe end, by tightening the ring nut, the latter is translated towards the pipe, the two clamping surfaces are drawn mutually closer and the pipe is tightly secured, also due to the gripping action exerted by the two steps on the inner and outer surfaces of the pipe to be connected.

Although these known pipe fitting elements can effectively achieve their purpose, they have a few serious drawbacks. Typically, the steps provided on the clamping surfaces of the ring nut and of the sleeve have a considerable radial projection, whereby the pipe is strongly deformed upon clamping. Hence, said pipe must be made from a highly deformable material to prevent fluid tightness problems or even ruptures of the pipe. Tightness is a critical problem, and the

operator can run the risk of excessively tightening the ring nut and of damaging the pipe. Further, these known pipe fitting elements have a very poor adaptability to different pipe thicknesses, hence a pipe fitting element with specific dimensional features must be provided for each pipe wall thickness and for each pipe diameter.

Therefore, the invention has the object to allow, by simple and inexpensive means, the provision of a pipe fitting element of the above described type, allowing a tight, non-unthreadable connection, with an end of a pipe to be connected, having at least equal, or even better characteristics than prior art pipe fitting elements, and further allowing effective clamping of the pipe, while avoiding an excessive deformation thereof. A further object is to allow the provision of a so-called"multifit"pipe fitting element, i. e. able to be used, with no ring nut or sleeve replacement, for connection of pipes having different thicknesses, without requiring, like prior art ones, a joint with different characteristics based on the thickness of the pipe in use.

The invention achieves the above purposes thanks to a pipe fitting element of the above described type wherein said clamping surfaces consist of progressive widenings of the outside diameter of the fit-in tubular sleeve and of the inside diameter of the ring nut end turned towards the pipe to be connected.

These widenings of the outside diameter of the tubular sleeve and of the inside diameter of said ring

nut end may be progressive in the ring nut tightening direction.

Hence, the pipe may be clamped between two annular surfaces, one in the ring nut and the other in the tubular sleeve at said progressive diameter widenings.

These progressive widenings of the tubular sleeve and of the inner surface of the ring nut may have such a progression as to form clamping surfaces having a substantially conical shape or similar. In other words, these clamping surfaces, regardless of their conformation, may have substantially conical enveloping surfaces.

The clamping surfaces provided on the tubular sleeve and inside the ring nut may be tapered in the same direction, i. e. widening towards the end of the pipe.

Advantageously, the clamping surfaces may have different tapering directions.

Further, they may have diverging tapering directions, i. e. the clamping surface provided inside the ring nut may be less steep than the clamping surface provided on the tubular sleeve. By this arrangement, as the thickness of the pipe to be connected increases, clamping between the ring nut and the sleeve may occur at decreasing diameters of the two clamping surfaces, hence different portions both of the ring nut and of the sleeve adhere to the pipe.

At least one of the two clamping surfaces may consist of a succession of step-like widenings, but considerable advantages are obtained if both clamping

surfaces of the tubular sleeve and of the clamping ring nut consist of step-like widenings. These steps provide an effective grip on the pipe walls and effectively prevent unthreading thereof. Further, the progression of the step-like widenings ensures a progressive clamping of the pipe, which is thus gradually, but firmly secured, while avoiding the excessive deformations that occur when using prior art pipe fitting elements having a single step with a considerable radial projection.

These steps may be equal or different in number along the same axial length, in radial projection and in radial length.

According to a preferred embodiment of the invention, the step-like widenings provided on the two clamping surfaces consist of a plurality of annular surfaces having the shape of cylinders or of truncated cones, with equal or different taperings.

In accordance with a preferred embodiment, the clamping surface provided on the tubular fit-in sleeve may consist of a plurality of annular surfaces having the shape of cylinders or of truncated cones with equal axial lengths and steepness, whereas the clamping surface provided inside the ring nut may consist of a plurality of annular surfaces having the shape of cylinders or of truncated cones with equal axial lengths and, at least partially, with a decreasing steepness in the tightening direction. Thanks to the above characteristics the clamping surface inside the ring nut is less steep than the clamping surface

provided outside the sleeve, as desired.

The end portion of the ring nut turned towards the tightening direction may have a widening flare to facilitate the insertion of the end of the pipe to be connected into the ring nut. This ring nut may have, on the pipe insertion end, a diameter substantially identical to the outside diameter of the pipe threaded on the tubular sleeve and/or slightly greater than said outside diameter of the pipe.

The maximum diameter of the tubular sleeve may be slightly smaller than the minimum diameter of the clamping ring nut, so as to allow insertion of the ring nut on the tubular sleeve from the end of the tubular sleeve turned towards the pipe to be connected.

According to an advantageous variant, the maximum diameter of the tubular sleeve is not smaller than the minimum diameter of the ring nut, but slightly greater, within the limits the material has for the passage of the ring nut over the widening of the sleeve. Depending on the material in use, the differences between the maximum diameter of the sleeve and the minimum diameter of the ring nut are such that a slight interference between the sleeve and the ring nut is provided, which is to be overcome when the ring nut is placed in the operating position. This slight interference between the sleeve and the ring nut is advantageous to allow a mechanical and tight clamping even of very thin pipes.

The tubular sleeve may have an abutment or end-of- stroke surface for the inserted pipe, consisting of a step-like widening or of an annular radial shoulder.

This annular radial shoulder, as will be apparent from the description of the annexed drawings, may be provided between the origin of the clamping surface provided on the tubular sleeve and the origin of the threaded portion provided on the tubular sleeve, preferably in the vicinity of the latter.

Advantageously, the tubular sleeve may have, at the end turned towards the pipe to be connected, a tapering portion to form an outward lead-in area facilitating the insertion of the sleeve into the pipe.

Alternatively thereto or in combination thereof, the clamping surfaces provided on the tubular sleeve and inside the ring nut may have each, at least partially, a concave or convex shape, with equal or different concavities/convexities, and with the same or different directions.

The pipe fitting element which forms the subject of the present invention may have many different applications, and particularly it may be made of one piece or applied or screwed or clamped in any other manner to the inlet and/or outlet of a line or of a device or of a hydraulic or pneumatic component, such as a cock, a valve, a counter, or the like.

Moreover, the tubular sleeve may have, at the end opposite to the one inserted in the pipe to be connected, different means for coupling it to the inlet of a line, or of a device or of a component of hydraulic or pneumatic systems, for instance to allow quick disconnection of the pipe from the line.

According to a variant embodiment of the

invention, the clamping surface inside the ring nut may be defined by a continuous surface having a helical form with a progressively decreasing diameter.

This is applicable both with conical and cylindrical surfaces, as well as with step-like progressive narrowings. In this case, a continuous helical step is provided, with a progressively decreasing diameter, particularly in the direction opposite to the pipe to be clamped.

It may be arranged that the helical surface has a variable pitch or that a multiple helical surface is provided in the form of a multi-start thread.

The left-or right-hand thread is selected in accordance with the thread for coupling the ring nut to the sleeve and in such a manner that, when the ring nut is tightened on the sleeve, the helical clamping surface is also tightened on the pipe to be clamped.

According to a variant of this embodiment, the clamping surface inside the ring nut may also consist of an internal cylindrical or conical thread.

This thread may have a helical tooth with any section.

The thread may have a variable pitch.

The thread may also be of the multi-start type.

The pipe fitting element which forms the subject of the present invention may find advantageous application in providing a joint for connecting the free ends of two pipe segments, typically comprising a straight or curved cylindrical body. According to the invention, this tubular body may have, at each end, a

pipe fitting element like the one described herein and the tubular sleeves of each pipe fitting element may be parts of the tubular body, or extensions thereof.

Advantageously, this joint may include grasping and/or end-of-stroke means for the ring nut in the unscrewed/opened condition.

These means may consist of at least one annular radial flange or shoulder provided in the central part of the tubular body between the two pipe fitting elements.

The tubular sleeves of the two pipe fitting elements may have equal maximum outside diameters, for connection to pipe ends with equal diameters, or may have different maximum outside diameters, so that pipes with different diameters may be connected (reducing pipejoint).

In accordance with a further variant of the invention, the pipe fitting element may have at least one gasket on the tubular sleeve, for cooperation with the inner surface of the pipe fitted onto the sleeve.

Alternatively, the gasket may be provided in the inner surface of the ring nut and cooperate with the outer surface of the pipe coupled to the pipe fitting element.

Both the tubular sleeve and the clamping ring nut may be also arranged to have sealing gaskets cooperating with the inner and the outer surfaces respectively of the pipe coupled to the pipe fitting.

The gasket/s may be of any type, either with a polygonal, e. g. square section, and with a round

section, such as a 0-ring or the like.

A preferred embodiment provides at least one gasket on the tubular sleeve in the connection part or annular apex between the end taper and the adjacent clamping surface, there being provided an annular groove for accommodating the gasket in that part.

In this case, the gasket may form the step for passage to the annular surface with the maximum diameter of the clamping surface of the tubular sleeve.

In the ring nut, the gasket is advantageously situated in the end portion opposite to the end of the tubular sleeve.

In this portion, a step-like narrowing may be provided, against which the gasket abuts axially, or in said narrowing an annular groove for accommodating the gasket may be formed.

According to another variant, the gasket may form itself the clamping surface of the tubular sleeve, thereby replacing the conical or step-like widening portion at the end of the tubular sleeve.

The presence of the gasket is particularly advantageous when the pipe fitting according to the invention is used in combination with pipes having uneven wall thicknesses, e. g. pipes obtained by axially winding a tape and sealing two overlapping edges thereof. These pipes are known with the name of"tape" pipes, which are sold, for instance, by Nelson.

The pipe fitting element in accordance with the present invention also allows the provision of a joint for connecting two, three or more free ends of pipe

segments, particularly made of plastic. In this case, the joint may have two, three or more pipe fitting elements according to the invention, whose tubular sleeves are stably connected or connectable to each other, and may have equal or different maximum diameters.

Additionally, there may be provided a joint for connection between an end of a pipe, particularly made of plastic, and a threaded end of a pipe, particularly made of metal. In this case, the tubular body may have a threaded end with a traditional thread, whereas the other end may include a pipe fitting element according to the invention.

The above description clearly shows the advantages of the present invention, which consist in that a pipe fitting element of the above described type may be provided, which allows an effective connection and sealing of pipes, particularly made of plastic. These pipes may be clamped between the walls provided on the clamping element without being excessively deformed, thereby avoiding the above mentioned drawbacks like fluid leakage and pipe damages. Further, thanks to the taper of the clamping surfaces provided on the tubular fit-in sleeve and inside the ring nut, pipes with different thicknesses may be connected by using the same type of pipe fitting element. A further advantage finally consists in that a smaller number of types of pipe fitting elements is industrially produced, whereby production is simplified and costs are reduced.

The further characteristics and possible

improvements of the invention will form the subject of the dependent claims.

The characteristics of the invention and the advantages derived therefrom will appear more clearly from the following detailed description of the accompanying figures, in which: Fig. 1 is a side view of a pipe fitting element according to the invention in the open condition, i. e. with the ring nut being completely translated in the direction opposite to the tightening direction.

Figs. 2,3,4 and 5 are exemplary side views of a straight connection joint having two pipe fitting elements according to the invention, the ring nut of one of these being in the extracted condition, whereas the ring nut of the opposite element is shown in tightened conditions on pipes of increasing thicknesses.

Fig. 6 shows an enlarged half of a joint.

Fig. 7 is a view like the ones of figs. 2 to 5 with the ring nuts being removed.

Fig. 8 is an enlarged detail of a ring nut according to a variant embodiment of the invention.

Figs. 9 to 14 show several different variant embodiments, wherein a gasket is provided at the clamping surface of the sleeve and/or of the ring nut.

Referring to the figures, a pipe fitting element in accordance with the invention comprises a tubular sleeve 1 fitting into a free end of a pipe 2 to be connected. The pipe fitting element which forms the subject of this invention is particularly suitable for

being used in combination with plastic pipes, thanks to the advantageous deformability characteristics provided by this material, but the use thereof is not to be intended solely restricted to the combination with pipes made of this material.

This tubular sleeve 1 has a preferably cylindrical inner axial space 3, for the passage of the fluid carried by the pipe 2. The tubular sleeve 1 has a maximum diameter D1, which is substantially equal to, particularly slightly greater than the inside diameter of the end of the pipe 2 to be connected, so as to allow the insertion of the sleeve 1 into the end of the pipe 2 with a slight resistance. This sleeve 1 further comprises, at the end part towards the pipe 2 to be connected, a section 4 which tapers towards the pipe 2, to facilitate insertion of the sleeve 1 into the pipe 2. The axial extension of this section 4 and its external shape may anyway be arranged to be different from those of the truncated cone-shaped section 4.

Immediately upstream of the truncated-cone shaped section 4, with respect to the direction of insertion of the sleeve 1 into the end of the pipe 2, there is provided the clamping surface 5 which is designed to be in contact with the inner wall of the pipe 2, when the pipe fitting element is in the mounted condition. In the figures, the truncated cone-shaped section 4 and the clamping surface 5 are arranged to be adjacent, but an intermediate tubular, for example cylindrical, section may be provided, having the function, for example, to strengthen the connection area.

This clamping surface 5 consists of a succession of widenings of the outside diameter of the sleeve 1 in the direction of insertion into the pipe 2 and particularly consists of a plurality of truncated cone- shaped annular surfaces 105 having equal tapers. In the figures, there are three annular truncated cone-shaped surfaces 105, but their number may vary also depending on the axial extension of this clamping surface 5 and/or on its total steepness. The larger base of each truncated cone has a diameter which is slightly smaller than the one of the smaller base of the adjacent truncated cone, with respect to the direction of insertion of the sleeve 1, whereby the clamping surface 5 consists of a succession of step-like widenings 105 which form a stepped surface 5 for gripping to the inner surface of the pipe 2, as will be described in greater detail below.

The sleeve 1 also has a cylindrical section 6 ending at an annular radial shoulder 7 which forms an abutment or end-of-stroke surface for the pipe 2 threaded onto the sleeve 1 (see fig. 2 and following figures). A threaded section 8 starts from the shoulder 7 and ends at another radial shoulder, formed by an annular end-of-stroke flange 9 for the ring nut 10 in the unscrewed/opened condition (fig. 1).

The ring nut 10 is coaxial to the tubular sleeve 1, and has on its outer surface a plurality of projecting elements, in the form of axial ribs or crests 11 to facilitate the grip for tightening it by hand or with the help of a tool. On the inner surface,

the ring nut 10 has a threaded section 12, whose thread matches the one 8 provided on the outer surface of the tubular sleeve 1. Downstream of said threaded section 12, with respect to the tightening direction, there is provided the clamping surface 13 of the ring nut 10, which is designed to be in contact with the outer wall of the pipe 2, when the pipe fitting element is in the mounted condition. This clamping surface 13 of the ring nut 10 consists of a plurality of step-like widenings 113, which are progressive in the tightening direction.

Like in the first clamping surface 5, these widenings 113 also consist of a plurality of annular truncated cone-shaped surfaces, but in this case they have decreasing steepnesses with respect to the tightening direction so that it may be stated that the two clamping surfaces 5,13 have substantially conical enveloping surfaces, and that the clamping surface 13 of the ring nut 10 has a less steep enveloping surface than the enveloping surface of the clamping surface 5 provided on the sleeve 1. As noted above, the steps 105,113 of said clamping surfaces 5,13 may be equal or different in number along the same axial length, in radial projection and in radial length. It may further be arranged that these clamping surfaces 5,13 have each, at least partly, a shape differing from the one described above, e. g. concave or convex, with equal or different concavities/convexities, and with the same or different directions, and even possibly cylindrical.

The outermost truncated cone-shaped surface of the ring nut has a much lower steepness than all the

others, thereby forming a widening flare 213 to facilitate insertion of the pipe 2 into the ring nut 10. To this end, the diameter of the ring nut 10 on the side wherein the pipe 2 is inserted is substantially identical to or slightly greater than the outside diameter of the pipe 2 threaded on the tubular sleeve 1.

Figs. 2 to 5 show a straight joint for axial connection of two free ends of pipe 2. This joint has a tubular, particularly cylindrical body 14, and at each opposite end thereof there is provided a pipe fitting element according to the invention. In the figures, this tubular body 14 is straight-shaped, but it may also have a different shape, e. g. for providing curved fitting joints. The tubular sleeves 1 of each pipe fitting element are part of the tubular body 14 of the joint, or axial extensions thereof.

In the intermediate portion between the two pipe fitting elements, the tubular body 14 has an element for gripping the joint, by hand or with the help of a tool, so that the introduction of the sleeves 1 and the tightening of the ring nuts 10 are facilitated. This gripping element consists of the two end-of-stroke flanges 9 for the two ring nuts 10 in the retracted/unscrewed condition, and of a third intermediate flange 15 having the same characteristics as the other two. The three flanges 9,15 are interconnected by axial strengthening ribs 16. The above described gripping element, which also has the function to strengthen the central part of the joint,

may also have any other shape deemed to be suitable, e. g. a transverse polygonal section, or even be missing.

In the figures, no pipe is connected to one of the pipe fitting elements, and the ring nut 10 is shown in the position in which it is wholly extracted from its sleeve 1. In the operating condition, the ring nut 10 is threaded on the sleeve 1. This may occur thanks to the fact that its minimum diameter is slightly greater than the maximum diameter of the sleeve. However, in order to ensure that very thin-walled pipes are clamped in a tight manner and with a sufficient mechanical strength, advantages are obtained from arranging that the minimum inside diameter of the ring nut and the outside maximum diameter of the sleeve are substantially identical, or anyway that the outside maximum diameter of the sleeve is slightly greater than the minimum inside diameter of the ring nut. The use of an intrinsically yielding material allows to force the ring nut into the operating position onto the sleeve, when it has to be threaded thereon, whereas the slight interference allows to effectively clamp in a tight manner and with mechanical firmness pipes with very thin walls. In the operating condition, the ring nut 10 is threaded on the sleeve 1, and wholly tightened so as to be completely translated towards its end-of-stroke flange 9. Here, the sleeve 1 can be inserted into the end of the plastic pipe 2, with a slight deformation 102 thereof due to the maximum diameter D1 of the sleeve being slightly greater than the inside diameter

of the pipe 2. The sleeve 1 penetrates the pipe 2 until the latter abuts against the annular radial shoulder 7 of the sleeve 1. Now, the ring nut 10 is translated by being tightened towards the end of the pipe 2, the two clamping surfaces 5,13 are drawn progressively closer to each other until the clamping surface 13 of the ring nut 10 comes in contact with the outer surface of the pipe 2, clamping it against the clamping surface 5 of the sleeve 1. It has to be noted that the pipe 2 is clamped between annular surfaces which are part of the two clamping surfaces 5,13 and that, as the thickness of the pipe to be connected 2 increases, clamping between the ring nut 10 and the sleeve 1 occurs at decreasing diameters of the two clamping surfaces 5, 13, hence different portions thereof adhere to the pipe. The different tapering angles of the ring nut and of the sleeve ensure a progressive clamping of the pipe, which is hence clamped in a gradual manner. By this arrangement, pipes with different thicknesses can be connected by the same pipe fitting element, without replacing the ring nut 10 and/or the sleeve 1. The steps 105,113 provided on the two clamping surfaces 5, 13 exert on the inner and outer surfaces of the pipe a gripping action and prevent it from unthreading therefrom. Where the deformability of the plastic material of the pipe 2 allows to do so, these steps 105,113 may form small steps on the surfaces of the pipe, i. e. little notches for restraining the pipe 2.

As is clearly shown in the figures, clamping occurs with a non excessive deformation of the pipe 2, while

the possibility of cuts or ruptures thereof is avoided and the sealing action of the pipe fitting element is improved as compared with prior art ones, which have a single cylindrical step.

Figs. 2 to 5 show, by way of example, the pipe fitting element according to the invention in combination with pipes having different thicknesses.

However, it has to be noted that the joint in accordance with the invention may also be used for pipes having even slightly differing diameters.

According to a variant embodiment of the invention as shown in fig. 8, the clamping surface 113 inside the ring nut 10 may be defined by a continuous surface having a helical form with a progressively decreasing diameter. Particularly, the different annular portions of the clamping surface 13 of the ring nut 10 are separated by a conical helical line 313.

The clamping surfaces 113 may be either conical or cylindrical. In the latter case, a stepped narrowing or form will be provided. Nevertheless, the stepped form is also applicable to conical surfaces 113. In this case, a continuous helical step is provided, with a progressively decreasing diameter, particularly in the direction opposite to the pipe to be clamped.

It may be arranged that the helical surface has a variable pitch or that a multiple helical surface is provided in the form of a multi-start thread.

The left-or right-hand helical surface is selected in accordance with the thread for coupling the

ring nut to the sleeve and in such a manner that, when the ring nut is tightened on the sleeve, the helical clamping surface is also tightened on the pipe to be clamped.

In accordance with a variant of this embodiment, which is not shown in detail but may be clearly understood by those skilled in the art based on the above description, the clamping surface 13 inside the ring nut 10 may also consist of an internal cylindrical or conical thread. This thread may have a helical tooth with any section. The thread may have a variable pitch.

The thread may also be of the multi-start type.

The clamping surface 5 of the tubular sleeve 1 may be also provided in accordance with the variant of fig.

8, and this alternatively to or in combination with an identical or similar construction of the clamping surface 13 of the ring nut.

The pipe fitting element which forms the subject of the present invention finds specific application in the conduction of fluids, particularly water, and particularly for irrigation fluids, but may be also used in other types of systems, e. g. designed for the supply of gas, oil or the like or for pneumatic systems.

With reference to the variant of figs. 9 and 10, a gasket 30 is associated to the clamping surface 5 of the tubular sleeve 1. The gasket 30, for instance made of rubber or of a plastic material similar to rubber, is in this case in the form of an 0-ring.

The illustrated embodiment provides, without

limitation, but as a preference, the application of the gasket 30 in the connection area between the clamping surface 5 of the tubular sleeve 1 and the end narrowing 4.

In the case of fig. 9, the gasket is accommodated in a groove formed in the step 105 with the maximum diameter and projects therefrom, forming a further step.

However, in the case of fig. 10, the gasket rests axially against a step 31, formed in the portion with the maximum diameter of the end conical taper 4 and forms at the same time a progressive widening, or the only progressive widening of the sleeve towards said portion with the maximum diameter of the end taper.

Figs. 11 and 12 show the use of a gasket 30' having a polygonal, particularly square section. In this case, fig. 11 shows a situation like that shown in fig. 9, whereas fig. 12 shows a conical portion of the clamping surface 5 of the tubular sleeve which ends by the step formed by the gasket 30'.

In both cases, the gasket 30'forms the last widening step of the clamping surface of the tubular sleeve 1.

Obviously, the solutions as shown and described for the 0-ring also apply to the gasket with a square or polygonal section and vice versa.

Figs. 13 and 14 show a pipe fitting in which both the tubular sleeve 1 and the ring nut 10 are provided with a gasket.

The gasket may be also only provided on the ring

nut 10 and not on the tubular sleeve 1.

The position of the gasket 30 and 30'on the tubular sleeve is as shown in the previous figures.

The gasket 32 associated to the ring nut 20 is accommodated either in a groove formed in the radially narrowest portion of the clamping surface 13 as shown in fig. 13, with a non limiting reference to the 0-ring gasket 32, or said gasket is axially adjacent to the clamping surface 13 of the ring nut 10 on the inner side thereof and abuts against an inner step 33 formed by said clamping surface 13. In the example as shown in fig. 14, the gasket still forms the annular band with the smallest diameter of the clamping surface 13. As noted herein for the tubular sleeve 1, the two embodiments are applicable indifferently both for 0- ring gaskets 32 and for gaskets having a polygonal, particularly square section 32'.

The invention is not limited to the embodiments described herein but may be greatly varied. For example, the clamping surfaces may consist of a succession of cylindrical step-like widenings. Also, the fitting element may be made of one piece or applied or screwed or clamped in any other manner to the inlet and/or outlet of a line or of a device or of a hydraulic or pneumatic component, such as a cock, a valve, a counter, or the like. Further, a joint may be provided for connection of three or more pipe ends, by arranging that the sleeves are stably interconnected or interconnectable. The outside diameters of the sleeves of the pipe fitting elements provided on the joints may

have the same diameter or different diameters. The joint may have different connecting means at one of its ends, such as a traditional thread. All this without departure from the guiding principle disclosed above and claimed below.