Locking Diesel Fuel Cap, Kenworth FTA-C-442L
Safety chain and crossbar included. Designed for use only on vehicles equipped with properly vented fuel systems. Non-Vented Cap, 3.5"- 5.5NS Threads. Measures 3.337" across threads.
Use the key to unlock the cap (the key won't come out when it is unlocked) then screw the cap onto the filler neck and turn the key to lock it. When you turn the key the cam will hit the side wall of the fill neck and bite in. It is very important not to over tighten the cap... Do not over tighten the cap when you screw it on.