Extra-heavy-duty open metal shelving units are bolted together for superior strength and rigidity compared to lower duty-level shelving. They are designed to hold very heavy equipment such as dies, fixtures, and jigs. Standalone shelving units cannot be expanded with add-on units, but you can place multiple standalone units side-by-side. Each shelving unit includes posts and shelves, with the posts forming a frame and the shelves bolting securely onto the posts.