120/277V clamp-on breaker lockouts are easy to install using thumbscrew design - no screwdrivers needed! Simply tighten lockout securely onto switch tongue, pull cover over thumbscrew and lock cover to prevent clamp from being loosened. Accepts lock shackles up to 9/32" in diameter. Made of rugged polypropylene and impact modified nylon. Cleats are included for use with breakers with long, sliding switch throws.