These are a connection that is very easy to over-tighten. Just make it snug and then give it a little more effort. But not too much. If you tighten it too much, you can feel the flared end of the tubing squishing a little bit.
Squishing it doesn't damage the connection and it doesn't cause a leak. But later on you often find the sucker is really hard to break loose. <--- No chit, right?
