It is composed of a hinge which allows a metal lever, or knife, to be lifted from or inserted into a slot or jaw.

Multiple knives may be attached to a single handle and can be used to activate more than one circuit simultaneously; this is a multi-pole switch.

Though used commonly in the past, knife switches are now rare, finding use largely in science demonstrations where the exposed mechanics of the switch make its function and state visually apparent.

The knife switch is extremely simple in construction and use, but for any dangerous electrical supply its exposed metal parts present a great risk of electric shock, and the switch is subject to arcing when opened at higher voltages, which poses a further risk of shock or burns to the operator and can cause fires or explosions under certain conditions.

These devices also prevent injury due to accidental contact, as all of the current–carrying metal parts of the switch are surrounded by insulating guards.