Lockout Safety Supply 120/277V clamp-on circuit breaker lockout fits circuit breakers 9/16 W x 3/8 L. The lockout measures 1-3/8"H, 2l, 7/8 inch W and accommodates 1 padlock, with shackles up to 9/32". the thumbscrew feature allows the device to be installed quickly and easily. The lockout is made from durable plastic (polypropylene) and nylon.