The propellers used for control-line models are commonly made of wood (usually maple), fiberglass-reinforced plastic (GRP), or graphite/kevlar/fiberglass and epoxy. The propeller pitch and diameter are chosen based on the engine size, type of performance desired, and cost. A typical .61-sized piped engine uses a 3-bladed propellor around 12-13" in diameter and around 4" of pitch, and is usually made of graphite/epoxy. A .20-sized sport model might use an inexpensive 8" diameter, 4" pitch propellor made of fiberglass-reinforced plastic. The graphite stunt propellers are usually made in small production runs or even by hand, and can cost as much as $50. Small GRP sport propellers are made by injection molding and may cost as little as $2.