Fiberglass reinforced nylon round belt idler pulleys (sheaves). Most come with 6203 ball bearings (17mm ID bore). Our B and C section V-belt pulleys can also work well as round belt pulleys. All pulleys can accommodate groove sleeves to increase their ID. Our 5/16" and 3/8" pulleys are standard round pulleys with low sidewalls/flanges. Our 1/4" pulleys have high sidewalls. All pulleys will work with belts thinner than the rated size. Click here for more info on our round belt idler pulleys.