WHK 150 PACK 1/2"PEX A Fittings PEX Expansion Rings PEX Ring Fittings 1/2 Inch Tubing Rings/Sleeve for Pex A Pipe.The 1/2 pex expansion sleeve is made of high quality polyethyleny material and certificared ANSI/NSF-61 and ASSE 1061 standard,it is more safe and confident to use 1/2 pex expansion fittings to connect 1/2 inch Pex a pipe or pex fittings( Pls note that NOT use to apply PEX b pipe),It is only use expansion tubing/pipe.The pex-a fittings has end stop design which is use to place a proper position to fit pex a pipe with tight and NO Leaks.The pex a fittings is widen to use hot and cold water,when you use them,it need to use professiona Pex a expansion tools to expanding the hole of pex a pipe and connection.