Nylon rollers, 2-inch wheel, 13-ball bearing, bag of 10. Three stem options: 4-inch, 5-inch, or 7-inch. The 13-ball bearing is the upgrade over the 11-ball, gives you smoother rolling and longer life because the load is spread across more contact points. They are the go-to for most residential replacements if you want quiet operation without going to steel. The 5-inch stem is less common but some builder-grade doors use it, so measure what you've got. Ten rollers handles a standard single door.