wedge

In mechanics, a device that tapers to a thin edge, usually made of metal or wood, and used for splitting, lifting, or tightening, such as to secure a hammer head onto its handle. The wedge is considered one of the five simple machines. Wedges have been used since prehistoric times to split logs and rocks; for rocks, wooden wedges, caused to swell by wetting, have been used. In terms of its mechanical function, the screw may be thought of as a wedge wrapped around a cylinder.