Part 26 washer/spring is just a Spring washer.
A ring split at one point and bent into a helical shape. This causes the washer to exert a spring force between the fastener's head and the substrate, which maintains the washer hard against the substrate and the bolt thread hard against the nut or substrate thread, creating more friction and resistance to rotation. Applicable standards are
ASME B18.21.1,
DIN 127B, and
United States Military Standard NASM 35338 (formerly MS 35338 and AN-935).
[9]
Spring washers are a left hand helix and allow the thread to be tightened in a right hand direction only, i.e. a clockwise direction. When a left hand turning motion is applied, the raised edge bites into the underside of the bolt or nut and the part that it is bolted to, thus resisting turning. Therefore, spring washers are ineffective on left hand threads and hardened surfaces. Also, they are not to be used in conjunction with a flat washer under the spring washer, as this isolates the spring washer from biting into the component that will resist turning. Where a flat washer is required to span a large hole in a component, a
nyloc nut (nylon insert) must be used.
The use and effectiveness of spring lock washers has been in debate of late,[
when?] with some publications[
who?] advising against their use on the grounds that, when tight, the washer is flat against the substrate and gives no more resistance to rotation than a normal washer at the same torque. NASA researchers have gone as far as to say "In summary, a lockwasher of this type is useless for locking."
[10][11] However, a spring washer will continue to hold the bolt against the substrate and maintain friction when loosened slightly, whereas a plain washer will not.
