New Dual Purpose Design acts as an Universal Coupler Lock as well as a Universal U-Lock! 360 degrees of solid steel protection against trailer theft. The UMAX50D is constructed of solid hardened steel and heat treated aluminum. It fits most coupler sizes (1 7/8" to 2 5/16"). A 5/8" (16mm) hardened steel shackle helps ensure your trailer is secure, even when left unattended. It has a patented dual locking system and a rust proof hammer tone epoxy finish for extra security.