The Perko Fuel System Locking Cap, part number 1324DP0BLK, is designed for securing non-vented fuel fills with a 1-1/2" opening. This black plastic cap includes a built-in lock cylinder and an integrated gasket. It is specifically engineered to fit Perko fill models 1313 and 1399. The cap's outside thread diameter measures 1-15/32 inches. It provides a straightforward solution for maintaining fuel system integrity on applicable machinery or vehicles.