wedge · split · screw · spiral · thread
The wedge is a powerful simple machine with a thin, pointed edge. Wedges are used to split, cut, or hold objects apart. A knife is a wedge that cuts through food. A nail is a very small but important wedge used in construction. Wedges can also be used as a doorstop to keep a door open. The screw is a simple machine with a spiral groove called a thread that wraps around a cylinder. Screws are used to attach objects to wood or walls, drill holes, and seal bottles. A spiral staircase is also a real-world example of the screw.