Varmint Guard Fan Pipe Cap with Screen - Fits 4" Pipe Alllows radon gas to escape, but keeps pests and debris out. Fits standard Schedule 40 4" PVC. Instructions: 1). Use smooth clean cut or factory end of pipe where guard will be installed 2). Place the stainless steel mesh on the end of the pipe 3). Fit the molded plastic part on the end of the pipe and over the mesh 4). Install the two stainless steel screws