Special Features:

Spec calls this: washer, countersunk, for use with bolts and nuts up to and including 260 ksi flu

Properties:

A washer of any peripheral shape having a centrally located hole. Both bearing surfaces are parallel and flat, but one or both of the bearing surfaces must be broken by a counterbore, countersink, or similarly shaped recess. The thickness must not exceed 25 per cent of the outside diameter or the largest outside dimension. The maximum limit of the tolerance or range applied to the thickness and/or largest outside dimension must be used to determine compliance. Excludes washer, concave, retainer, packing, and thrust type washers. See also spacer, sleeve; and spacer, stepped.