Hole is round with flats width across flats is 0.189 in.
A bent spring metal washer with a centrally located hole. It is designed to exert pressure axially when assembled in place.
Classification: Copper washers including spring washers not threaded
NSN 5905-01-431-0933
NSN 5855-01-542-2016
NSN 5975-01-525-7252
NSN 5835-01-090-0784
NSN 5930-01-557-4237
NSN 6685-01-324-4710
NSN 5960-01-293-1571
NSN 5945-01-541-4827
NSN 5950-00-918-7594
NSN 6145-01-291-4252
NSN 5999-01-561-3096
NSN 6685-00-296-0392