If you need these push-in fittings with metal, please choic these.
They are also in different shape, and only one hand can be very convenient to insert the tube and pull out without any
tools. The fittings with safty sealing and it's thermostable. 
In addition, these pipe fittings meets repeated insertion and pull-out requirement, when it getsolder along with the timed, this series can easily be replaced.
Reliability:  Rapid manual connecting and disassembling.
Compatibility: Works with the use of nylon, pu, teflon tube.
Adaptability: Hot and cold water systems, steam machine tool, lathe.
Varify the diameter and the thread to adapt to your tubings.