The Premium is our flagship straight lift, rated for 350 lb and folded to just 10.5″ — the narrowest profile in the industry. The Heavy Duty is engineered for higher weight (600 lb capacity, industry-leading) with a wider chair, stationary armrests for stability, and a reinforced footrest. Both use the same patented grease-free worm drive. If you need higher weight capacity or a wider seat, choose the Heavy Duty. Otherwise, the Premium is the right fit for most homes.