Single plastic pulley is made of one plastic sheave assembles on a steel frame with brass axles and rivets.
The sheave can spin freely and the pulley has hooks on both sides.
Two, single plastic pulleys can be combined to form a fixed/moveable block and tackle pulley system. These pulleys have sheaves with deep V-grooves with diameters of 50 mm.
Pulleys are often used as parts of compound machines. They function as helper machines, easing the lifting power. In fact, a pulley system can cut the force necessary to lift a very heavy object in two, four, etc., depending on the designed system. With these pulleys you can study and measure the force and distance trade off with compound machines. These pulleys are good for science experiments as well as functional tasks.