Master Lock 646 combination locks are padlocks that feature a 13/16-inch metal lock body and steel shackle. The lock body has a black finish and the steel shackle a silver or gold finish. The locks are designed to secure luggage and travel gear, professional carry cases and bags and jewelry and curio-style cabinets. Master Lock 636 combination padlocks use a three-digit, resettable combination. No matter the model -- for example, Master Lock 646T or 646D -- the method for changing the combination is the same.
Turn the dials on your Master Lock 646 combination padlock to your combination or the "000" factory default.
Pull up on the shackle to open the lock.
Turn the shackle a quarter turn -- 90 degrees -- counterclockwise.
Push down on the top of the shackle and turn it another 90 degrees counterclockwise. While holding the shackle in this position, roll and align the dials to the new combination.
Reverse the shackle 90 degrees clockwise and then lift it up.
Return the shackle to its normal position with the shackle end above the hole in the lock body. Close the shackle and scramble the dials.
Move the dials to the new combination and pull up on the shackle to confirm that the new combination works.