Zurn PEX® XL-Low Lead Brass Barb Coupling. The QQC_GX is used to connect two separate pieces of PEX tubing. Manufactured from EcoBrass®,C69300. These fittings, as a system with Zurn PEX® tube, are pressure rated at 160 PSI at 73 deg F, 100 PSI at 180 deg F, and 80 PSI at 200 deg F. These fittings are listed by NSF as complying with the following standards NSF/ANSI Standard 14, NSF/ANSI Standard 61 including Annex G, ASTM F877, CSA B137.5, and ASTM F1807.