This is a 12mm equal push fit tee piece connection. This fitting is specified to be used with reverse osmosis systems, fridge filters, and pneumatic units.
There are numerous material types this part will work in conjunction with. These include tubing (as well as flexible tubing like silicone and Tygon®, although soft tube supports will be needed), soft metals (copper, brass, mild steel) and semi-rigid plastics (nylon, polyethylene, polypropylene).
Constructed with food safe materials that have been approved by WRAS, ANSI, SK Zert, NSF-51 and NSF-61.