With the exception of the changes concerning the threading, the proportion and the quality of the materials utilised, the nut has ever since enjoyed a monolithic structure. Nevertheless, the evolution of new technologies and the use of new materials requires a more flexible and adaptable tool according to consequential and specific needs of employment.

The nuts normally used for functions similar to those of the captioned nut are defined "self-locking". Such nuts are manufactured in different shapes and use various locking systems (polyamides rings, spring rings or peculiar shapes or flutes at the end of the nut). Their common feature is the monolithic structure and the fact that the locking action starts to operate from the very first approach of the locking part of the nut to the screw thread. The locking action is constant during the whole screwing phase and remains identical during the approaching phase to the supporting surface; as a matter of fact, it does not depend upon the tightening torque and even in case of complete tightening the locking value of the nut over the screw (referred to the locking effect) is equal to the starting value.

The contact area concerned by the locking effect touches only a small part of the threads surface connecting nut and screw. in such a way that the pressure on the threads is concentrated on a limited area both on the screw and inside the nut. and the main part of the nut, for its whole thickness, works like a normal nut (without there being any locking effect).

In this case. some inconveniences occur, such as difficulties in the screwing phase for long stretches. need to use. in the screwing phase (in particular cases). loads not compatible with the resistance of the supporting surface (that might be damaged), impossibility to graduate the locking effect, constraints in the choice of the manufacture materials of the nuts, limits to the employment possibilities for particular purposes of physical. chemical and mechanical resistance.

In the following outline, the terms "locking'' and 'tightening" shall have the meaning indicated hereinbelow: - blocking: action exercised by the bush upon the nut thread; - tightening: action exercised upon the nut during the screwing phase at the end-turn screw.

General features The captioned self-locking nut in the shape and structure described hereinbelow in Drawings, provides for the solution to the above referred problems.

The nut (figure nr. 1) is made up of two different parts: an external part (the handling ring - figure nr. 3) and an internal part (the bush - figure 2). Such parts are peculiarly designed in the internal resting frame of the handling ring which is complementary to the truncated-cone bush. Furthermore. the bush is characterised by the existence of an axial longitudinal cut aimed to allow the elastic locking system to work.

Such design allows the threads of the bush to combine in a gradual and progressive way with the nut threading, thus guaranteeing the self-locking effect of the nut.

In terms of structure, it is possible to design the contact surfaces related to the handling ring and the bush in such a way as to guarantee different mechanical effects.

There are two different structures: a) locking structure with low tightening torque - in order to satisfy the need not to exercise high pressure loads over the supporting surface, over the internal surface of the handling ring (figure nr. 3) and over the external surface of the complementary bush (figure nr. 2), which are designed to be perfectly adjacent: such surfaces are characterised by a definite degree of roughness that allows the rotating ring to trail the bush by way of adherence until the occurrence of the "clutch effect" caused by the friction coefficient and cone shape of the touching surfaces.

b) locking structure with high tightening torque - in order to satisfy, instead. the need to exercise high pressure loads over the supporting surface.

the existence of a drag tooth located in the internal surface of the handling ring (figure nr. 6) and the complementary existence of a cavity in the bush for such tooth has also been devised (figure nr. 5).

The predisposal of a high degree of roughness or. alternatively, of microgrooves on the internal contact surfaces of the two parts (ring/bush) causes: - in the event under a), a limited sliding movement between the touching surfaces with the consequent decrease of the tightening torque (caused by the delayed "clutch effect"); - in the event under b) a decrease in stress over the handling ring and the drag tooth.

Such solution allows the locking of the nut both axially and radially in the joints or screw fixings, with a variable locking load, arising from the amount of pressure on the supporting surface of the nut while tightening. The possibility of locking even at low tightening torque values makes the system particularly suitable for mixing structures composed of materials of different quality and type, materials of low hardness, thermoplastic and thermosetting resins and for connecting all structures made of materials with low specific contact pressure.

It is not excluded an use, in tightening with middle or high preloading, in combination with structures composed of materials of higher hardness.

Once the tightening is complete, there can be further lockings and programmed unlockings.

The shape of the nut, in two parts, allows the assembling with the two components made of different material in kind and with different physical.

chemical and mechanical resistance features. The combinations of the possible assembling (nut) in ferrous and not ferrous materials allow a wide employment range in the most different exercise conditions.

In case the nuts are manufactured with an hexagonal shape, as far as design and dimension are concerned, they are interchangeable with other nuts of ordinary employment with normal and large key.

The maximum axial and radial locking load, working on the screw thread, by means of the nut, is determined by the stretch value of the screw at the end-turn screw and it operates from the moment of the first contact of the nut with the supporting surface.

The solicitations on the self-locking nut are lower than the limits of resistance to stress of the materials by which it is made of. Such solicitations allows the system to interact in elastic field, stabilising the self-locking effect without permanent deformations.

This specific self-locking effect improves the adherence between the contact surfaces of the nut thread with the screw in those cases in which the particular manufacture of the kind of material used is of a low friction coefficient.

Drawings The self-locking nut, of hexagonal shape, is represented by the drawings attached herein in the two manufacturing versions with identical working principle: version nr. 1 collects figures nr. 1, 2, and 3, version nr. 2 collects figures 4, 5, and 6 Version nr. 1 locking nut with low tightening torque figure nr. 1 Version nr. 2 locking nut with high tightening torque figure nr. 4 It is made up of two parts assembled together in a one-piece structure ready for use with ordinary handling devices.

Part A) - Elastic cone bush with nut screw function.

Part B) - Handling ring with bush housing.

Part A) - Cone bush figure nr. 2 without nut checking cavity in figure nr. 1 figure nr. 5 with nut checking cavitv in figure nr. 4 Cone bush with threaded hole and longitudinal axial cut for elastic system with slack of threads'fitting.

The bush, with or without checking cavity for drag tooth is lodged and locked in a stable way in the cone-shaped housing in the handling ring.

Type, shape and dimension of the thread under provisions in use applying the metric system and others.

Part B) - Handling ring figure n. 3 without nut drag tooth in figure n. I figure n 6 with nut drag tooth in figure n. J Ring with cone-shaped cavity to allow housing of the bush, with or without drag tooth.

The size and the external shape (and therefore dimensions) of the ring are in compliance with unified systems for a standard employment with normal tightening devices.

The handling ring may come in shapes different from the hexagonal one. and therefore the self-locking system is adaptable to any tightening device with a threading system.

Instead. should the locking occur with clamps, the handling ring may not be present. In this case it might be necessary to devise a truncated- cone cavity located in the part to be connected, so as to allow the housing of the complementary threaded bush (in this instance, references could be made to self-locking thread).

Working Conditions During is screwing phase. the nut runs free on the thread, until it reaches the supporting surface, and the angular shifting of further tightening makes the bush run in axial direction "Q" in the cone-shaped cavity of the handling ring.

The value of"Q" run (see Version nr. 1, figure nr. 1 and Version nr.

2, figure nr. 4) is a result of the different sizes (thickness) of bush and ring.

The system (Screw thread - angular shifting of the nut - bush run - cone fitting of bush and ring) causes the normal slack between tolerances and functioning of nut/threads and 'the clamp self-locking effect" on the screw arising from the radial load of the fitting bush/handling ring.

The blocking undergoes a progressive process, ever since the first contact between nut and supporting surface happens, with a secure combination of the geometrical shape of nut screw (bush) and threads, without an overdue load in case of locking with nut just resting or tightened lightly.

Double structure (and alternative) of the self-locking system according to the same working principle: 1 .Low tightening torque - See Version nr. 1.

Nut without drag tooth = locking load over thread according to tightening torque with maximum value assessed by the clutch effect between cone- shaped surfaces when touching - nut screw bush.

2.High tightening torque - See Version nr. 2 Nut with drag tooth = locking load over thread according to tightening torque with maximum value assessed by the resistance to yield stress of the materials which constitute the nut.