Am I missing something here?

I bought 2 3/8" compression fittings the other day at home depot. They are 3/8" tubing to 1/2" FPT pipe. This is so I can then connect my QD's to my CFC. I brought them home and went to put them on my 3/8" OD copper tubing I made my CFC out of and was pretty surprised when there was no "compression" and the fitting just slid over the tubing. I know there is a chance that if I torque down on it, it will compress onto the tubing, but before I do that I thought I would check.... did I forget something????

There should be a ferrule inside the nut on the 3/8th side. The ferrule is a metal band that slips over the tube. It is captured by the compression nut. When you screw down the nut, it ferrule is deformed to make a tight seal.

If you don't have the ferrule, it won't compress.

Some compression fittings also have a tube insert to support the tube on the inside. There isn't much need for it on a copper tube.

Ok, the tightening and deformation was the part I was confirming. I was all set to take it back to HD but if I tested it by torquing down on it, it wouldn't be returnable.

Appreciate the info