These replacement sheaves can be used for a lot more than just replacement for your pulleys.  You can create your own pulley system or even your own pulley. Diameter is 50mm, Bore is 3.5mm, Accepts ropes smaller than 4mm in diameter.

These sheaves are perfect for science projects and experiments.  They have a diameter of 50 mm and come in a pack of five.

This compound machine was designed and built using five of the sheaves.  It demonstrates the lifting power of these home made pulleys.  Pulleys are often used as parts of compound machines such as this one. 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.