The airsoft piston body is a hollow block placed over one end of the main spring to give the sector gear in the gear set something to grab onto. It has a row of teeth that run along the length of its body that mesh with corresponding teeth on the sector gear which convert rotational power from the electric DC motor into a linear pulling force on the main spring.
The piston body is typically made up of two parts, the tooth or teeth rack, and the piston body itself. The piston body can be shaped differently and can be composed of different materials depending on its intended purpose. It has railing tabs on the side which slot onto the railing lugs on the gearbox shell that guide its motion. The metal tooth rack can cover any number of teeth with the minimum on stock pistons being one single tooth at the release end. Others may opt to cover half the number of teeth in metal, or the full length from the pick up end up to the release end. The total number of teeth however, may vary depending on the version of the gearbox, some of which require longer pistons.