PREMIUM QUALITY MATERIAL--These U-Groove Bearings are made of high quality material, which are durable and wearable enough to ensure a long lasting performanceOFFERS WORKING PROCESS--There are internal lubrication grease in the U-Groove Wheels, which can provide a operation and good mute effectU SHAPE DESIGN OFFER BETTER PERFORMANCE--These Pulley Rail Ball Bearings adopts with a U-shape design, which have surface to reduce frictionHIGH-VALUED PACKAGE--There are total 4 pieces of pulleys in one set that you many use for many projects upon your purposesWIDELY APPLICATIONS--These U-type Pulleys have widely applications during daily life, and they can be widely used in doors and windows to track and drive mechanical equipment.Features:Made of high quality material, these pulleys are durable, sturdy and wearable.Internal lubrication grease, operation, good mute effect.U-shape groove design, surface reduces friction.There are total 4 pieces of pulleys in one set that you many use for many projects.Widely used in doors and windows to track and drive mechanical equipment.Specifications:Model: 0840UUType: U-grooveMaterial: Metal, plasticColor: BlackInner Diameter: 8mm/0.3inOuter Diameter: 40mm/1.6inThickness: 20.7mm/0.8inQuantity: 4pcPackage Includes:4 x Pulleys