So ... apparently THANGORODRIM is a group of three volcanic mountains ...
and it's also an anagram of HANG DOOR TRIM!
3. Did they have RUBBER BANDS in Middle-earth? It's possible- - the stuff comes from trees!
Or REGGAE BANDS?

Bet some of the Rangers liked them.
I'd guess RANGERS, but I'm not sure if there were three bands of them.
I wonder if one of the answers is to do with the three lines of succession in Arnor.
Hang on ... is 3 just RINGS? Bands of precious metal? Sings with R for right, or arguably spelt wrong?