Prime-Line Products M 6154 Tub Enclosure Roller, 7/8-Inch Flat, 4-Pack 7/8 in. diameter flat edge nylon ball bearing Threaded hex hub 4 wheels with screws Fits most J shaped tracks 7/8 in. tall 7/8 in. diameter flat edge nylon ball bearing 4 wheels with screws Fits most J shaped tracks 7/8 in. tall