The combination padlock is usually made with a metal "can" with three tumblers inside connected to a dial on the front. The mechanism is very similar to that used in safes. When the correct combination is entered, the notches on the tumblers line up and allow a latch to fall into the notches, releasing the shackle. Combination locks of this type are not recommended for outdoor use because they can fill up with rain water which causes them to rust. The laminated padlock is constructed from a series of metal plates that are riveted together. 