Galvanized Steel Neoprene Sealing Washer.
Sealing Washers are a thin conically shaped round steel stamping with a centered hole. It is bonded to a rubber/neoprene piece slightly smaller in outside and inside diameter. When these washers are assembled with screws the rubber offers a protection against leakage. This reduces the chance of the fastening becoming loose due to vibration, and minimizes damage to the surface for which it is being attached.