Although locks come in different shapes and sizes, most of them are based on a similar concept. The cylinder lock is considered the most common design in use. For this type, the key once inserted into the hole will turn the cylinder or plug. In return, this turns an attached cam. Whenever it is turned one way, the cam will pull on a bolt and the door will open. However, if the plug is turned the other way, the cam will release the bolt and a spring will snap it back into place and the door will not open.
Inside the cylinder type, the correct key will be able to solve the puzzle inside the lock. It is important to understand more about the way they are designed. The most common design is the pin and tumbler locks. The main components of this type are the pins. They come in various lengths and are divided into pairs. Each pair is located in a shaft that runs through the central cylinder plug and into the lock housing. The springs found on top of the shaft keep the pins in position. When there is no key inserted into the lock, the bottom pin is found completely inside the pug while the other pin is found halfway in the plug and the housing. When it is inserted, the notches will push the pins up into different levels. With the right key, the pins are pushed just enough to make the pair of pins line up perfectly.
A master key operates several locks. Basically, there is nothing special about it, but the lock itself. These locks are configured in a certain way that will be open with two or more keys that are different from each other. Locks that come with a master version are designed with a second set of mechanism that is used to operate them. For instance, a master keyed pin and tumbler lock come with two shear points at each pin position. One point is for the change key while the other is for the master key.