I am doing a hardline tubing build using Bitspower Multi-Link hardline compression fittings. What I have not seen before is inside each package for a fitting is a separate O-Ring. There is already an O-Ring in the fitting when you unscrew it that you place over the hardline tube and if you try to put the extra O-Ring in there, then it doesn't screw down for the seal securely. So, what is this separate O-Ring in the package for? Is it just a spare if you need one and not used?Thanks.