[GMGQ]

Also, there are different brands/types of fittings. Some are shiny, some have amatte finish, some are light grey, some are dark grey. It depends on where you get it from. I've had some that would only go in 1/4 of the way, and others that go all the way in.

So you may want to try another type of the same fitting.

And no matter what type, you should alwayswrap some teflon tape around the threads for a better seal (I usually do at least 3 layers).