The side-float design uses a float on the end of a lever to control the fill valve. The float is usually shaped like a ball, so the mechanism is often called a ball-valve or a ballcock (cock in this context is an alternative term for valve; see, for example, stopcock). The float was originally made from copper sheet, but it is now usually plastic. The float is located to one side of the main valve tower or inlet at the end of a rod or arm. As the float rises, so does the float-arm. The arm connects to the fill valve that blocks the water flow into the toilet tank, and shuts off the water when the float reaches a set height. This maintains a constant level in the tank.