Steel or stainless steel.

Steel electro zinc-plated, hardness ≥ 465 HV 1.
Stainless steel hardness ≥ 520 HV 0.05.

These lock washers ensure that bolts and screws subjected to transverse loads, chattering or vibrations do not work loose. A joint is also secure at low levels of tension. If the bolt (nut) tends to loosen independently in bolted joints under dynamic stress, the bolt (nut) carries its positive-locking washer with it, the sloped surfaces of which run directly up against the angled surfaces of the counter-washer. In other words, the more a bolted joint tries to loosen itself, the more securely the wedge action of the washer blocks the attempt.

Supplied glued together in pairs.