This is a first cam check assembly for the 2 1/2 - 4" Ames 4000SS & 5000SS assemblies. Simply unthread your old cam check and thread in this brand new complete cam check assembly. Includes a new cam check O-ring. Genuine Ames repair part. No special tools are required for servicing but a handy cam check tool is available to assist in removal and replacement of the cam check assemblies.