McMaster 91812A724 Extreme-Vibration-Resistant Wedge Lock Washer, 316 Stainless Steel, for M20 Screw Size, 0.840" ID, 1.210" OD

When it's critical to keep bolted assemblies secure, choose these two-piece lock washers with the tightest grip of all. They stop nuts and screws from loosening in heavy machinery that experiences jarring starts and stops, such as compressors and compactors. Serrations on the outside bite into the fastener and mating surfaces, while wedges on the inside lock the two pieces together. When the nut or screw starts to loosen, the wedges drive more tightly together to maintain tension. You can reuse these washers up to fifteen times, as long as the serrations and wedges are not worn down. They are comparable to NORD-LOCK® or Sherex TEC® washers.

Highly Corrosion-Resistant 316 Stainless Steel—Superior to 18-8 stainless steel, these washers won't degrade when exposed to harsh weather, salt water, and most chemicals.

Top-and-Bottom Serration—Adds friction for extra gripping power.