Retainer washers for Caster Wheels are often made with specially designed inside diameters to allow the washer to easily slide into place and grip the outside of a screw shank, bolt, spanner bushing, or product component. These washers are generally assembled with a screw or spanner to make the final assembly process more efficient. In the case of caster wheels, a retainer washer will have an outside diameter to fit the outer diameter of the wheel bore size. Then, the inside diameter will usually be the same size as the Spanner Bushing or Delrin spanner bushing used inside the wheel. Great for keeping all of the caster wheels components in place and secure from moving at all times. Retainer washers come in both plastic and metal depending on your caster wheels application and requirements.