The shelves are wide enough to hold a CAP 70 lb. kettlebell. Starting at 50 lb. and decreasing by five pounds, I was able to fit six kettlebells on the rack. If I placed the 70 lb. and 60 lb. on a shelf I was limited to two kettlebells per shelf.. Assembly consists of securing the shelves to the uprights with the provided eight bolts and nylon locknuts, sixteen washers and a hex key. Use a 17 mm or 11/16" socket to tighten the nut while securing the bolt with the hex key. In a pinch a crescent wrench will do. Seems very sturdy and well built.