Hydraulic or pneumatic cylinders inherently produce linear motion. Torque control can be pneumatic or hydraulic. Factories also used hydraulic and pneumatic power. Manual, spring, electrical, pneumatic, and hydraulic. Starters can be electric, pneumatic, or hydraulic. The barrels are rotated by an external power source, usually electric, pneumatic, or hydraulic. The interconnections can be realized by various means, such as mechanical, hydraulic and pneumatic. These suspension modifications are in contrast to lowriders, which use hydraulic or pneumatic suspensions. An air compressor for powering pneumatic tools is included. See the airgun article for information on how spring piston and pneumatic airguns work. The bolt features a telescoping return spring guide which serves as a pneumatic recoil buffer. Stage separation occurs via reusable separation collets and a pneumatic pusher system. Early rubber tires were solid (not pneumatic). A hybrid combines principles of the combustion and pneumatic spud gun. V AC outlets, and a compressed air outlet for pneumatic tools.