Bike Boltz 8 Nord Lock 5/16" M8 8mm Vibration Proof Lock Washer - Tension Tighting Fasteners 8 Pairs (16 Total) of genuine Nord-Lock brand lock Washer Fits 8mm or 5/16" bolts, screws, and other fasteners For Use With Grade 5 & Grade 8 Bolts and Metric Grade 8.8, 10.9, and 12.9 Bolts. Through Hardened: Min. 44HRC, Max. 51 HRC Uses precision geometry to secure fasteners from slipping. Tightens by tension rather than friction for a better, more secure grip Dimensions: 13.5mm (17/32) Outer Diameter, 8.7mm (11.32)Inner Diamter, 2.7mm (5/64)Thick(when paired together)