These are 3-inch steel rollers with 10-ball bearings, sold in a bag of ten. The 3-inch wheel is for doors running on 3-inch track, which you'll mostly see on commercial or heavier residential setups. They're built to take more weight than the 2-inch version and roll solid on wider track. Stem options are 4, 7, 9, or 11 inch, so pick whichever matches your hinge setup. Steel rollers are louder than nylon, just so you know. Before ordering, confirm your track is actually 3-inch and not standard 2-inch residential.