The QUICK FIST XL clamps are not only our largest size, but they are also our strongest clamp. They provide a safe working load of 150lbs (68kilos), and a break-strength of 300lbs (176kilos) per clamp. Two clamp sets support up to 600lbs (273kilos). QUICK FIST XL holds objects up to 15” (381mm) in diameter or about 30” (762mm) in a linear direction. QUICK FIST clamps are made in the USA of heavy duty transportation grade rubber and are not affected by hot or cold climates or salt. The rubber is uv resistant.