airline fittings Are Generally Designed To Be Used With Air Lines Some Small Air Fittings Work With Polyethylene And Other Plastic Tubing Used In Water Filters, Aquariums And Ice Makers. However, Push Connect Fittings Usually Can't Be Used With Flexible Copper Tubing And There's A Large Variety Of Air Tube Fitting In The Market; In Fact, You Can Find Air Fittings D.I.Y Stores Push-Fit Pneumatic Fittings Grip The Attached Pipe With A Stainless Steel Ring That Has Teeth Inside The Fitting While The O-Ring(S) Ensure A Watertight Seal Around The Pipe. However, If The Edges Of The Pipe Aren't Perfectly Round Or Have Dirt On The Surface, It's Possible That The O-Rings Don't Make A Tight Seal And Cause Leakage. Similarly, If The Pipe Isn't Cut In A Perfect Square, It May Not Push In Evenly Inside The Fitting. That's Why It's Important To Use A Tubing Cutter To Cut The Pipe—Never Use A Hacksaw How To Install A Push Lock Fittings Other Than Using An Appropriate Tubing Cutter For The Pipe, Also Make Sure To Measure The Cut—Remember That The Attaching Pipe Will Extend Inside The Fitting Use A Deburring-Depth Gauge Tool To Indicate The Depth Of The Fitting And Then Push The Pneumatic Fitting Onto The End Of The Pipe To Attach It