Selecting the correct coupling requires a balance of pressure ratings, material compatibility, and movement requirements. Buyers must distinguish between Rigid Couplings, which provide a permanent grip to prevent any movement, and Flexible Couplings, which allow for thermal expansion, contraction, and angular deflection. Always verify that the housing material (typically ductile iron ASTM A536) and the gasket grade (EPDM for water/steam or Nitrile for oil/gas) match your specific medium and temperature range.