Can't put gems in socketed item

[Guest]

I found a 3 socket short bow in Act1 (single player), and I had a few spare gems and a jewel. I thought it would make a nice bow for my merc, so I tried to stick them in. None of them would go inside the bow. It made a twanging sound whenever I tried.

I picked up a socketed cap, and tried it. It wouldn't go in either. I meet the level requirements for the jewel/gem. What's going on?