THESE ARE SIEMENS ECQL1 CIRCUIT BREAKER LOCKS TO KEEP IMPORTANT CIRCUITS ( LIKE ALARM, OR SUMP PUMP) CIRCUITS FROM INADVERTENTLY BEING TURNED OFF. THEY WILL NOT STOP THE BREAKER FROM TRIPPING JUST MAKE SOMEONE THINK TWICE ( AND BRING A SMALL SCREWDRIVER BEFORE TURNING OFF A PROTECTED BREAKER ) THEY ARE GREAT FOR PROTECTING ALARM CIRCUITS OR SUMP PUMP CIRCUITS OR ANY OTHER BREAKER YOU DON'T WANT ACCIDENTALLY TURNED OFF. THEY FIT MOST ITE / SIEMENS AND MURRAY BREAKERS, BRYANT, GE, CUTLER HAMMER BR ( not tan handles) T B, CHALLENGER HOME LINE BREAKERS (std ones not Sq D) ABOUT THE ONLY BRAND OF STANDARD BREAKER THEY DON'T FIT IS THE FEDERAL PACIFIC STAB LOC'S AND SQUARE D QO. IF YOU WANT TO KNOW IF THEY FIT A PARTICULAR BREAKER MESSAGE ME AND I WILL TRY AND CHECK IT OUT.