In GB 2, I 84,509A, we have described threaded fasteners having indicating means responsive to a change in a diameter or other transverse dimension of the fastener for indicating when a selected value of stress has been attained in the fastener, during tightening. One example of fastener described is a bolt and nut wherein a threaded end portion of the bolt is hollow and contains a pin which, when the bolt is unstressed, is free to turn relative to the bolt but, when the bolt is stressed in tension to its elast ic li mit, is gripped by the bolt so that turning of the p ^* π relative to the bolt is no longer possible. It is suggested that freedom of the pin to turn relat 've to the bolt can be checked by means of an al ien kev introduced into an appropriate socket in o head of the pin.

It is an obiect of the present invention to prov'de a more convenient way of indicating when the bolt disclosed 'n the aforesσ ^; d publ ished application has been stressed to its elastic limit.

According to a first aspect of the present invention, there is provided a tool suitable for use in turning a nut on a bolt and includ'na. an outpu+ member through which, when the tool is in use for turn ^' nq the nut. torque ^; s transmitted to the nut, a sensing element arranaed for at least li mited turning relative to the output member about an ax ^; s defined bv the output member, transmitt ina means for transmittina toraue to the sens ^' nq element to turn the sensing element with the output member and ind ^; cat ^; na means for indicating when the output member turns relative to the sens a e lement.

The sensing element is preferably arranged to l ie on the axis of th<= output member and adapted to co-operate in torque transmitt ng relation with a pin mounted in a threaded end portion of a bol t, onto which end portion a nut is to be driven by means of the tool.

The output member mav define a socket to receive the nut. in whic case the sensinq element is preferably access ⁱ ble through the socket. Al ternatively, the outDut member mav compr ^' se a D lvanna! lug for rece ^; v ^; nc a separate socket component, such QS ^' S common! ¹ / used ^'■ - co^'u cfon v.' ^; t wrenches. In the latter case, the sens ^* na elem ^c orotπ 'de bevond _

free-end of the lug to enter α socket component, when the latter is fitted to the lug.

The sensing element is preferably movable along the axis of the output member relative to that member against the action of biasing means. Accordingly, as the nut is driven along the bolt the output member can advance with the nut, without carrying the sensing element along the bolt.

The indicating means may be adapted to provide a visual indication when the output member turns relative to the sensing element. A visual indication may be provided mechanically, for example by the relative movement of two components. Alternatively, the visual ind ^r cation may be provided by an electrically energisable indicator. Additionall ^y or alternatively, the indicating means may be adapted to provide an audible indication and may comprise an electrically energisable sound source.

According to a second aspect of the invention, there is provided a too! suitable for use in turning a bolt or nut and having an output member through which, when the too! is in use for turning a bolt or nut, torque is transmitted to the bolt or nut, a sensing element arranged for at least li mited turning relative to the output member about an axis defined by the output member, a handle, means for transmitting drive from the handle to the oufou+ member, means for transmitting drive from the handle to the sens ^: ng element and indicating means for indicating whether or not one of the output member and the sensing element turns relative to the other.

According to a third aspect of the invention, there ^; s provided a too! suitable for using in turning a bolt or nut and hav ^' ng an output membe" through which, when the tool is in use for turninq a bolt or nut. torque is transmitted to the bolt or nut, a sensing element arranged for at least limited turning relative to the output member about an axis defined by the output member, transmittina means for transmitting torque to the sensing element to turn the sensing element with the output member and indicating means for indicating when the output member turns relative to the sens ^' ng element, wherein the sensing element has a socket suitable for receiv ^τ ng an end portion of a pin protruding from a bolt when the too! ^: s used for turnmg the bolt or for turninq a nut on the bolt.

There is also provided in accordance w ^: th the present ^: nvent ^: on a method of turning a nut on a hollow, threaded end oo>-t ^; on of c bolt ^ich conta ⁱ ns a pin arranged for turning relative to the holt about a-~ ax ^; s of the thread, wherein the pin and the nut are turned toσe+ er relat ⁱ ve to the bolt

until the bolt is subjected to α predetermined tensi le stress, as sa'd stress is attained, the pin is gripped by the bolt to restrain turning of the pin relative to the bolt, turning of the nut relative to the bolt and the pin is continued, a signal is derived from turning of the nut relative to the pin and turning of the nut is then discontinued.

The signal may be a visual and/or audible signal provided to a person control ling the operation of tightening of the nut. Alternatively, the signal may be applied automatically to discontinue operation of a machine which is tightening the nut.

Examples of tools embodyinq the present invention and which are used in a method according to the present invention w ^; ! l now be described, with reference to the accompanying drawings, wherein:-

FIGURE I shows an end view of a first tool;

FIGURE 2 show? a cross-section of the first tool on the l ine !!-!! of Figure I ;

FIGURE 3 shows a bolt ond a second tool, both the bolt and the too! being shown partly in cross-section;

FIGURE 4 shows internal parts of the second tool, as viewed along on axis defined by the second tool; and

FI GURE 5 shows diaqrammatical ly a cross-sect ion of the second tool in a plane containing the axis.

The tool of Figures I and 2 is intended for use ^' n transmitt ina drive to a polygonal nut and includes a general ly cyl indrical output member ' 0 havina at one of its ends a socket I ! of a suitable size and shape to receive the nut with a sliding fit. The external surface of the member 1 0 is a surface ^f revolut ion about a longitudinal axis 1 2 of the member. The membe addtionally has surfaces which are other than surfaces of revolution about this axis and which are thereby adapted to transmit torque to a further member. for example a nut. The form and disoos ^; tion of these torque- transmitting surfaces is selected according to the form of a nut or other member to be driven by the tool. 3v way of example, an exagon _ ' socket i shown. The longitudinal axis I ? of the output member ' 0 co ^' nc ^' des with an axis defined bv the socket I I . The output member is adapted to rece ^' ve rotary drive from a polygonal drivina lug ⁽ not shown ⁾ of c k own wrench. Genera l ly, wrenches have a drivma luc of sauare shape i transverse coss-

section. Accordingly, the output member is provided at ^' ts end remote from the hexagonal socket I I with a square socke r 13 suitable for receiving the driving lug of a known wrench. The outpu . member fits onto a known wrench and transmits drive therefrom to a nut in the same manner as do know" socket components used with wrenches. The output member can be used for driving a known nut onto a known bolt.

The tool illustrated in Figures ! and 2 is intended primarily for driving c nut 9 onto a bolt of the kind illustrated in Figure 3. This kind of bolt has a hollow, threaded portion 1 5 to receive the nut and a pin 1 6 mounted in the threaded portion of the bolt. An end portion of the pin protrudes from the bolt and is adapted to engage in a torque-transmitting manner w ^; th a sensina element 17 of the too! of Figures ! and 2. In the particular example illustrated in Figure 3, the profrudina end portion of the pin has the form of an enlaraed, non-circular head. A shank of the pin 16 extends into the bolt with sliding clearance so that the pin is free to turn relat ^' ve to the bolt, when the bolt is unstressed. A circϋp or other means mav be provided to retain the pin in the bolt. The bolt is disclosed in GB 2.184,509. published 24-th June ! 987.

The too! i llustrated in Figures t and 2 is hollow along its ent ^' re length. Between the hexagonal socket I ! and the sauare socket ! ~. there is _ cylindrical chamber 1 4 which contains the sensing element ^{! 7} . Between the sensing element and the square socket 1 3. there is fitted ^: nto f^ chamb ^r c plate 18 which is fixed with respect to the output "- be ^r '. ^' -. A co ^' Sed compression spring ! ? acts between the plate 13 and the sens ^" ng element i ~ to urge the sensing element resϋiently towards the hexagonal socket 1 . . The sensing element ! 7 has at its end adϊacent to the socket ! I a recess having c size and shape which are complementary to the size and shape of the head ?< ^" > of the pin \ 6. One or other of the head 20 and recess 2 ! mav be flared, to faci litate entry of the head into the recess. The sens ^: ng element lies on the axis 12.

The chamber 1 4 also contains a sleeve 22 which receives the sens ^' nc element 17 with a sliding fit. ^τ he sens ^' ng element σ ^~ ϊd the sleeve are keved together so that relat ^' ve axial movement ^" s perm ⁱ tted but ""e!c ^{+ '} ve turn ^' nc about the axis ! 2 is prevented. A pin 2.1 extends th'-o a^ a hole ^' n t e sleeve and an end portion of the o>n ^' s rece ^r vec w th clearance in a cx ^: σ!'v extending groove formed in the sensina element ~ ct the pe O^e ¹ "-' t e ^r eo ^x . Co-ooerat ^; on between the end porf ^; on of the p ^; n GΠC f s ^' des _ ' * ^k e σ ^r oove

prevents turning of the sleeve relative to the sensing element about the axis 1 2. The pin 23 extends from the sleeve 22 in a direction awav from the ax ^' s 1 2 through a slot formed in the output member 10 to a further sleeve 24 mounted on the outside of the output member. The pin 23 is fixed to the sleeve 24 so that this sleeve is constrained to turn about the axis ' 2 relative to the output member ! 0 with the sleeve 22 and the sensing element 17.

The sleeve 24 constitutes indicating means for indicating to a user wher turning of the output member 10 relative to the sensing element 17 occurs. To this end, the sleeve 24 is formed with several windows which are spaced apart around the circumference of the output member 10 and through whic ^r corresponding parts of the external surface of the output member can be viewed. Turning of the sleeve 24 relative to the output member 10 is l i mited by the length of the slot in the output member throuqh which the pin 7~ extends. This slot typical ly subtends at the axis 1 2 an angle in the range 30 ^' to -0°.

Those parts of the external surface of the output member 1 0 which are exposed to view through the windows of the s leeve 24, when the pin 23 is at one end of its slot, may be coloured differently from those parts which are exposed to view when the pin is at the opposite end of its slot.

Transmitt ing means is provided for transmitting toraue between the output member 10 and the sensmg element 1 7. In the example il lustrated, the transmitting means ^; s capable of urging the sensing element into a datu°" position with respect to the output member ' 0. that datum pos ^: t ^' o ^r - corresponding to occupation of one end port ion of ^; ts slot bv the o ^! n 23. ^τ he part icular example of transmitting means i l lustrated in the drawma is c torsion spring 25. One end portion of the torsion sprina is attached to the sleeve 22 and the opposite end portion of the torsion spring is attached to the plate 1 8. During assembly of the components, the torsion soring is pre- stressed to ensure that the torsion soring exerts torque on the sleeve 22 in a ! ! positions of the pin 23 in its slot. This torque must be overcome in order fo the output member 10 to turn relotive to the sensing element 17. It wi l l be noted that the pin 23 prevents axial movement of the sleeve 22 w ^' th the sensing element ' 7 and thus prevents the tors'on sp ma 25 b<= ^: ng c ^r fected b relative axial movement of components of the tool. ^u 'hen the tool of Fiaures I and 2 is used to scew c nut o^to the bol t i llustrated in Figure 3. the output member 1 0 is f ^' tted ove ^r the nut G-.d the sensinq element 17 is u>'oed bv the sorinc ' onto the head 20 o ^£ the p ^; n s

that a torque-transmitting relation is established between the output member 10 and the nut and a torque-transmitting relation is established between the sensing element 17 and the pin I D . Torque is then transmitted to the nut via the output member 10 from a handle or from a power fool. The nut is screwed along the bolt by the applied torque and torque is also transmitted from the handle or power too! via the spring 25 to the sensing element ! 7 and thence to the pin ! 6 so that the pin is turned with the nut. The pin 23 remains at that end of its slot to which is urged by the spring 25.

When a predetermined tensile stress, for example that stress which corresponds to the elastic limit of the bolt, is established in the bolt, the bore in which the shank of the pin 16 is disposed contracts sufficiently for the bo!- ¹ to grip the pin and restrain continued turninq of the pin with the nut. As turning of the nut is continued, the sensing element 17 is held aqainst rotation by the pin ! 6 and the output member 10 turns relative to the sensing element. This is indicated to the operator by the appearance of dϊfferentiv coloured material in the windows of the sleeve 24. The operator then discontinues driving of the nut. The output member ! 0 is w ^; thdrawn from the nut, thereby withdrawing the sensing element 17 from the head of the p ^: n ' 6. The sensing element is then turned bv the spring 25 bock to its initial pos ^' tion with respect to the output member 10. ^τ he too! i llustrated in Figures 3. 4 and 5 comprses a bodv ' 26 havlnc a handle ! 27 which protrudes from and is fixed with resoect to the bodv. An output member ! 1 0 of the tool also protrudes from the bodv ' 26 but ^: n c direction which is perpendicular to that in which the handle protrudes. ^τ he output member ! 10 has external surfaces wh>ch are other than surfaces ^c revolution about the ax ^; s 1 ! 2 of the output member. ^τ he oart ^r cula ^r example of output member illustrated in the drawing is a sσuare lug hσv ^; ng the sa ^,Υ - size and shape as do the driving lugs of known wrenches. ^τ he lug ^; s mounter for turning relative to the bodv 1 26 about the ax ^' s ! 12 of the !ua and c ratchet mechanism may be incorporated in the body to control turning of the lug relative to the body. The lua 1 ! 0 is hollow and t ^κ e nternal surface of t lug may be a surface of revolution about the axis I ! 2.

A sensing element ! '7 is also mounted *n the bodv ' 2. fc turn'n- relatlve thereto about the ax ^' s ! 17. ^ _e sensmg element ! ^' -es o" ^' na* ax ^' s and extends through t e central ooen ^' na formed ^; n the d ^{r '} v ^' nc !vc M . he sensmq element protrudes somewhat bevond the dr ^" v ^' nq 'uc so V""z_ ^~ . as show- ^; n ^iqure 3, when a socket component 1 28 Is fitted to t ^' ^e ^■ ~ ^' '- ^' v ^τ -_a luc. * ^' "■'_

sensinq element can protrude into the socket component. The socket component may be a known component used with known wrenches. That end portion of the sensing element ! 17 which lies in the socket component mav have a demountable head 129. formed with a recess to receive the head 20 of the pin 1 . ^τ he sensing element 1 17 is connected with the body 1 26 in a simi lar manner to that in which the sensing element 17 is connected with the output member 1 0. Thus, the sensing element is free to undergo li mited axia! displacement relative to the body and the output member and is urged by a coiled compression spring ! 19 to move along the axis relative to the body in a direction towards and into the socket component 1 28. The sens ^' ng element ^; s also arranged for li mited turning relative to the body and output membe ^r and a torsion spring 1 25 is provided to oppose relative turning of the sensing element and body and to urge the sensing element towards a datum oos ^' t ion about the axis I 12 re lat ive to the body. The sensing element sl ides in and is keyed to a sleeve I 22.

The indicating means provided in the tool of Figures 3, 4. and 5 differs from the indicating signa l l ing means of the tool shown in Figures I and 2. in that the means of Figure 3 includes an electrically energisable light-source ! 30. This light-source is mounted on or in the body 126 where it will be conspicuous, during use of the tool. A battery for supplying e lectrica l po>.ve ^r to the light-source is contained in the body ! 26 and enera ^' saf ion of the I ^" qht- source is controlled by an electrica l sw ^' tch 1 3 1 . also mounted in the bodv and near to the axis ! 1 2.

For operating the switch 1 3 1 , there ^; s provided a rotarv cam; 1 32 which is connected with the sensing element 1 17 by the sleeve 1 27 to prevent turning of the sensing element relative to the cam but to permit axla ^: movement of the sensing element relat've to the cam.

When the tool of Figure 3 is used to tighten a nut on the bolt of Figure 3, the socket component 1 28 is fitted over the nut and the head 20 of the pin is received in the recess of the head 1 29. There is thus established a torque- transmitting relation between the handle 1 27 and the nut and a torque- transmitting relation between the sensing element I 17 and the pin 1 6. T e output member M O is turned bv means of the handle 1 2~ to dr ^' ve the nu ⁺ along the bolt. Torque is transmitted from the handle v ^: a the tors ^' on sprma ! 25 to the pin 1 6 to turn the pin with the nut. When there has been attained in the bolt a predetermined stress such that the bolt arlps the pin nn d

prevents continued turning of the pin, continued turning of the output member 1 10 results in turning of that output member and of the body 1 26 relative to the sensing element ! 17 and the cam 132. The switch ! 3 1 is carried by the body around the cam 132 so that the switch is operated by the cam and the light-source 130 is energised. This provides to the user a visual signal indicating that the required stress has been attained ?n the bolt. The user than ceases turning of the nut and removes the tool from the nut and bolt.

It will be understood that an electrically energisable light-source and a switch for controlling the light-source may be provided in the tool of F igures ! and 2, the switch being arranged to be operated bv turning of the sleeve 24 relative to the output member 10. For example, provis ^' on may be made for limited axial movement of the sleeves 22 and 24 and the slot in the output member 10 through which the o ^; n 23 extends may be inclined to the ax ^; s ! ? so that movement of the pin along the slot causes ax ^; a! displacement of the sleeve 24. The switch may be positioned in the path of travel of the sleeve. Modified in this way, the tool may be driven by a power tool, the sw ^; tch being incorporated in the power tool to control operation thereof automaf icallv.

It will be understood that, in a case where electricallv energisable signalling means is provided, this mav include an electricaϋv energisable sound source for providing an audible signa! to the user.

The too! of Fiqures 3, 4 and 5 may be modified for turn ⁱ ng a bolt, in a case where the hollow end portion of the bolt which contams the pin is that end portion which includes a polygonal head of the bolt. In suc a modif ⁱ ed tool, the means for transmitting drive from the handle to the sensmg ele en* is arranged to turn the sensing element relative to the output member. ^r o - example, a ratchet mechanism of the tool mav be arranqed to apply torque in one direction to the output member when the handle is turned in o direction and then to apply torque to the sensing element ^; n the opposite direction when the movement of the handle is reversed. As in the case of the tool described with reference to Figures 3, 4 and 5. the means fo ^~ transmitting torque to the sensing element would be adapted to vield whe the pin is gripped bv the bolt, and vlelding of the toraue-transm ^' tt m means would operate a switch to energise the light-source.

The features disclosed in the forego ^; nπ descr ^' ption. or the accompanying drawmqs. expressed in their spec ^: f ^; c forms o in er s of o means for oerformina the disclosed function, or a method or ^p rocess fo ^r

attaining the disclosed result, as appropriate, may, separately or in anv combination of such features, be util ised for real ising the invention in diverse forms thereof.