What hitec servo?
Hitec uses 2.5 mm threads I think. I drill mine out and tap them to 3mm so I can use any short screw in my spare parts box.
If you drill and re-tap it, be very careful not to drill or tap beyond the bottom as it will push the potentiometer inside the servo apart. I did that once.
Take a piece of wire, stick it in the servo bolt hole, mark it, then use that to mark your drill bit and tap to give you a guide.
I do this to all my metal geared servos so I don't ever get caught without a spare. Besides, the servo horn screws are always made out of super soft stock, so they strip easy and your still screwed.(no pun intended...)