The SharkBite UA23103A25 is a 3/4-inch plastic expansion sleeve - sold as a pack of 25 - designed specifically for use with PEX-A piping systems. It enables secure connections to brass or poly expansion fittings, forming joints that become tighter and more reliable over time. Installation requires a PEX expansion tool (and matching expansion rings), after insertion, the chamfered sleeve slides onto the tubing and the built-in stop ensures proper positioning. Certified under ASTM F-1960 and ASTM F-877 standards, this sleeve is approved for potable water service lines, burial applications (including concrete encasement), and radiant heating systems - and offers long-term durability thanks to its corrosion-resistant plastic construction and cross-hatch interior that helps prevent sliding or loosening.