The small diameter tubing (typically less than 1/4” OD), commonly used in laboratory instruments for transporting solvents, is often made from fluoropolymers like PTFE, PFA, or FEP. Due to their rigid walls, these chemically resistant tubes are not suitable for barbed connectors. Instead, they are attached to caps and manifolds using compression fittings. These fittings work by tightening a threaded nut over a pliable ferrule, compressing the tubing’s outer diameter to create a secure, leak-proof seal around the tube and at the bottom of the threaded port.

Type A (1/4-28) threaded fittings are made of polypropylene, while Type B (5/16-24) fittings feature ETFE ferrules with PEEK or Acetal nuts. Type C (1/8” NPT) and Type D (1/4” NPT) fittings include adapters to accommodate larger port sizes. For a reliable seal, wrap NPT threads 2-3 times with thread seal tape and wrench-tighten securely.
All compression fittings are color-coded to indicate the tubing size they are designed to fit.