Parker's hi-duty fittings are preassembled with the sleeve machined onto the nut. During assembly the sleeve breaks away from the nut and seals on the tubing. This unique design creates tight; leak free joints that withstand pressures of most commonly used types of tubing including seamless steel tubing, copper, Brass and thermoplastic tubing. This design also provides a vibration dampener which enables joints to stand up under moderate vibration.