The Plate Washer sits between the flange nut and the clamp in a T-slot clamping assembly. Its job is to spread the clamping force over a wider area than the nut face alone, which prevents the nut from dishing into the clamp surface over repeated use.

You’ll use this when your clamp doesn’t have a hardened top face, when you’re clamping soft materials like aluminium fixture plates, or when the setup needs extra load distribution — high-torque tightening on thin clamps, for example.