AN960 Flat Washer 0.438" OD, 0.203" ID, 0.032" Thick. 

AN960 flat washers are used under hex nuts to provide a smooth bearing surface, as shims to obtain the correct grip length for a bolt and nut assembly, and to adjust the position of AN310 and AN320 castle nuts with respect to drilled cotter pin holes in bolts and clevis pins. Available in regular and light thickness.