The Uponor R20 Compression Fitting Assembly threads onto manifold loop outlets. This R20 QS (Quick Seal) compression fitting connects Wirsbo hePEX™ or Uponor AquaPEX® tubing to the manifold in radiant heating applications and is designed for 5/16, 3/8, 1/2 or 5/8 in tubing. The R25 QS compression fitting does not directly thread onto the manifold, but onto other R25 connections, and is designed for use with 5/8 and 3/4 in tubing only.