Gas Turbine homebuilders usually use these on the compressor cover to attach all the fuel, oil, pressure and starting gas lines to the turbine. .If you don’t like push in connectors or want something a little bit more secure this is the way to go. The all aluminum design has a 5mm thread on one side and a barbed nipple with a blue anodized sealing ring (that goes over the tube) on the other. It is a very positive and secure connection method.
The through hole is 2.4mm in diameter (0.094”). It works great with 4mm O.D. Polyurethane tubing. It has a sealing washer on the thread side too (not shown).