Installing Grease Fittings?

[TexasLS1]

So this is a kindergarten-level question, but it's my first time replacing steering parts and therefore putting the new grease zerks on joints/tie rods. None of them are tightening very easily for me- in fact they're not even threading in. Am I supposed to be tapping threads before installing the fittings, or just forcing them in? I just hate the thought of screwing up new Moog parts that I just painted...