Clamp 1 up to 3/8" (10mm). Clamp 2 up to 1/2" (13mm). Clamp 3 up to 1" (25mm). Clamp 4 up to 13/4" (45mm). Ubolt type design,set covers many pipe sizes;. Makes clamping off fuel, vacuum, brake, heater pipes etc. very quick and easy.