RS PRO Red 1-Lock Lockout Polypropylene Single-Pole Breaker Lockout, 7 mm

This single pole circuit breaker lockout device is designed for use with 120 V breakers that have holes in the switch tongue.
Very simple to use - just snap the lockout device into place and lock with a lockout padlock (not included).
Dual cavities have been built-in to accommodate differently-sized switch tongues.