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.

With flat sides, these washers fit into slots and channels and won't rotate out of position. They are also wider and thicker than most round washers, so they distribute heavier loads across a larger surface area. Square washers are commonly used to anchor heavy machinery, fasten framing to floors, and hang pipe and conduit from strut channel.