The bearings which the gears run in.

Bushings are the bearings in the gearbox that allow the gears to spin.

Similar to Bearings, but with no moving parts Airsoft AEGs contain nylon Bushings that hold the axle for each gear in the gearbox.  These bushings allow the gears to turn easily without moving out of position.  For stronger powered springs, metal bushings are required.  For ultimate performance, Bearings can be used instead (like Bushings, but with small ball bearings inside the unit to reduce friction).

A mechanical device used as a lining for an opening to prevent abrasion to wire and cable. Also used as a low cost method of insulating, anchoring, cushioning and positioning. Usually a non-metallic material is preferred.