Arvid Nilsson 1353953 is a DIN 127B spring lock washer for M4 fastening, measuring 4.1 mm inside diameter, 7.6 mm outside diameter and 0.9 mm thick. Fabricated from zinc-electroplated steel with flat ends, it develops locking preload beneath a bolt or nut where vibration or thermal cycling could otherwise loosen the joint. Supplied in packs of 100.