A locker is a small compartment that is used to store things such as books, coats, etc. They are commonly found in schools. They are usually locked with a padlock or a built-in lock. Usually there is an array of lockers. Each user has his/her own key (or combination) and can not open other people's lockers. There is sometimes a master key used only by the manager which can open all of the lockers. The typical maximum padlock shackle thickness is 5/16 inch (8 mm), and the typical door thickness is 0.8 mm. High-security lockers typically have a 10 mm or more maximum shackle thickness and a 1.2 mm door thickness.