Screw clamps consist of a galvanized or stainless steel band into which a screw thread pattern has been cut or pressed. One end of the band contains a captive screw. The clamp is put around the hose or tube to be connected, with the loose end being fed into a narrow space between the band and the captive screw. When the screw is turned, it acts as a worm drive pulling the threads of the band, causing the band to tighten around the hose (or when screwed the opposite direction, to loosen). Screw clamps are normally used for hoses 1/2 in diameter and up, with other clamps used for smaller hoses.