Frame and supports: 1″ square aluminum tubing. Crossbracing runs side-to-side and front-to-back throughout height of unit. Side-to-side crossbracing have front-to-back oval tube laterals welded in place. These shelves are spaced 10″ apart and support bins by the bottom, allowing for a variety of sizes. Casters: 5″ diameter non-marking swivel stem casters with thermoplastic rubber tread. Shipped assembled.