Hey, I have a trem where there is a small allen key hole on the underside which locks the arm in place. However when I unscrewed the screw, only half of it came out...Is there any way I can get the rest of this out? I cant get the arm in as its locked, so the trem is unusable unless I can find a way to get it out.
take the guitar to autozone and ask them if they have a stud removal kit for a screw that small.
What you really need is a new...

Well, I have to deal with this many times a week in plumbing business. Normally we just drill it out, but since that would ruin the trem I suggest you do what the above user said.
- Gibson SG Standard
- Lag Roxane 500
- Eastwood Hi-Flyer
- Takamine EG523

- Jet City JCA50H
- George Dennis 60Watt The Blue Combo
- Marshall SuperBass 100Watt
how about a screw extractor?

I seen a more expensive one, with interchangeable heads... "Grabit" was the name brand I think? If you could find one that would work on not just the standard size screws, but also the smaller precision screws and allan keys (either as a set, or with interchangeable heads) would be the best. Especially on guitars and small electronics.