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Stainless Steel A2. For the majority of screw lengths the threads goes all the way to the head of the screw (i.e. l1= l2) less 2.5 thread pitches.
Threaded fasteners may unintentionally back-off when the assembly is in use. In certain circumstances this “failure” could lead to serious problems.
The self-locking fastener was developed to retain the advantage of re-usability whilst preventing the problems of accidental disassembly when pre-load is lost.
The self-locking fastener is designed to prevent the “backing off ” when the initial axial tension is lost. They resist rotation on the fi rst and subsequent installation and decrease the tendency of the fastener to fatigue by reducing the vibration transferred to the fastener.
The fasteners here work by wedging the fastener into close proximity with the mating thread, this is achieved by using an engineered plastic strip or pellet. Generally the longer the locking feature, the greater the fastener assembly locking torque (as more thread pitches are engaged).
The Locking strip is added by machine a specially formed narrow slot and adding the locking patch, this is held in place with adhesive. Independent tests show that the tensile strength of the fasteners are not adversely affected by the low profile milled slot for the locking strip.
For self-locking fasteners the standards IFI 124 and IFI 524 (for commercial applications) and MIL-DTL-18240 (for military applications) apply. Typically they are tested to be suitable for at least 5 installation/removals. The locking patches are generally a special nylon ASTM D-4066. Temperature range -50C to +120C, although a further strip type Vespel (brown) has a temperature range of -250C to +250C.
a temperature range of -250C to +250C. The locking strips must never be removed (otherwise its effectiveness is destroyed), and the inserts can be damaged by certain plating processes, so plating must never take place after insert installation.
Ensure the thread mating parts are in tolerance.
Countersink the female parts as shown below, to prevent damage to the strip on installation.
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