How to Change the 646D Masterlock Combination

Rotate the lock's combination rollers so that its current combination (set to 0-0-0 at the factory) lines up with the red stripe along the face of the lock.

Lift the shackle from the lock body and rotate it 1/4 turn counterclockwise so that the notch at the bottom of the shackle lines up with the small notch in the body of the lock. Press the shackle down into the body of the lock, and then rotate it another 1/4 turn in the same direction.

Turn the combination rollers to your new combination.

Rotate the shackle back 1/4 turn to align the notches, and then lift it from the lock body. Rotate the shackle another 1/4 turn so that you can return it to the lock body in its normal locked position.

Close the shackle into the lock body and randomly rotate the combination rollers to lock it in place. Rotate them to the new combination to open the lock.