Idlers are vital to the conveying process. They support the belt and conveyed material along its full length preventing it from stretching, sagging and eventually failing. They typically comprise a steel frame and 1 to 5 rollers, depending on application. There are two main categories: carrying idlers and return idlers. Carrying idlers (sometimes also called troughed idlers) support the belt that carries the material, while return idlers are designed to support the empty belt. Each of these categories has several sub-categories.