Light-duty applications will benefit from a lightweight and inexpensive plastic pulley. Before you go out to purchase one, however, be sure to determine exactly how you intend to use the plastic pulley and look for a size and function that will suit your needs. Pulleys can come in a variety of sizes, and the durability of the pulley can be affected by the grade of plastic used to construct it. Consider whether you want just a plastic pulley, or if you need other components such as an axle, frame, and so on.
In many cases, a plastic pulley is designed to be used with a certain diameter of rope or cable. Be sure to find out which is best for your pulley, and make sure the pulley and cable or rope will suit your needs. Pulleys may also be rated for weight, so if you intend to lift or move objects using the plastic pulley, be sure to take note of its weight limitations. Sometimes more than one plastic pulley can be used in a block and tackle system, increasing the amount of weight the system can carry or pull. Be sure to consider your weight requirements and buy the appropriate types and number of pulleys.
If you intend to mount the pulley to a wall, ceiling, or other fixed object, be sure to choose a pulley that features a mountable frame. This frame can be made from plastic as well, though it is a good idea to look for a plastic pulley mounted in a more durable metal frame that will not split, crack, or otherwise fail due to force being placed upon it. Whenever possible, purchase a pulley with a frame that includes mounting hardware so you can install the unit quickly and easily.
A block and tackle system may require a double pulley. This means two pulley wheels are mounted within a single frame, and the pulley wheels are able to rotate independently from each other. This increases the versatility of the unit, especially if you intend to use the pulley as part of a lifting system. Like other systems, the double pulley will need to be chosen based on its applications, as well as the size of rope or cable that will be strung through it. Look for hollowed or grooved pulleys that will help keep the rope or cable on track during use.