The main purpose of a mechanical device known as a slide block 16 line is to control an electrical circuit. Simple sliding motions are used to move the switch from an open position to a closed one or vice versa. It usually includes a pin or knob on each one that the key can engage. The key has one or more tracks on its sides that are used for this. The pins of the slider block 16 line on either side of the key fit into the track and are raised to the proper height when the key is inserted.