Plate flanges   fit over the end of the pipe and are typically installed with the flange face 0.375 in. (9.5 mm) beyond the end of the pipe. This allows for welding on both sides of the flange – one weld for strength is welded to attach the flange spigot to the pipe, and a seal weld is welded inside the flange at the end of the pipe. If service conditions permit, the seal weld is not made. Plate flanges are most often used at lower pressures – Class 150 (PN 20) or Class 300 (PN 50) pressure ratings are used.