RE: Servo screw sizes?
I think the OP is talking about the servo arm screw. If that is the fact, use the screws for that servo, Futaba, use futaba screws, JR, use JR or Spektrum screws, etc. The threads of the servo arm screws are different in each brand or servo. Do not force a screw into a servo it doesn't fit, you will strip it out, then you have to buy new gears. I would call the MFG of the servo, and order just that screw, however there may be a website to order online. Horizon Hobby is a good starting place.