3.6mm shackle diameter, shackle inner size is 20mm in width, 19mm in height. Durable Zinc Alloy construction.You can set and reset the combination padlock with hundreds of possible combinations, making it harder to crack.In addition to travel, this combination padlock can be used for various lockers, such as hostels, gym, etc.How to Reset:1.The lock is preset at factory to open at 0-0-0. check the 0-0-0 aim at indication line. Press down the snap. Now the lock is ready to open.2.Press down the button with sharp tool, hold the position until next step 3 is finished.3.Turn the character wheels to set your personal combination.4.Release the button, now your private combination is set.5.Remember well your new combination. If you want to change it again, please repeat.