diameter is .3125 grade 8 lock washer, standard.
A washer which is usually round with a centrally located hole. Its edges and two bearing surfaces are so designed that applied pressure brings into play the spring tension and/or frictional locking principle which materially resists any tendency toward turning. It may be made of one or two pieces
NSN 5925-01-439-1984
NSN 6610-00-977-9264
NSN 6135-01-423-7502
NSN 5996-00-574-3625
NSN 6150-00-253-3368
NSN 5835-01-013-9321
NSN 5975-00-387-6515
NSN 5999-00-064-2418
NSN 5975-01-518-4172
NSN 5855-01-180-2172
NSN 5965-00-204-8513
NSN 6220-00-176-5912