Hitec is 2.5

I found that out too!

When I first bought a hitec servo, I dropped the little screw and struggled to find one, had to put one of them self tapers in it, then started running airtronics and never thought about it again, then went to high voltage and found that same problem, but found them screws in bulk, just surprised they never changed to the 3mm

Thanks to everyone! I'll try all the ideas, and any other ideas that get posted. Will part #89009 (servo ring and washer) help at all, or just trying the M3 6-8mm and locktite be better?

That washer will just let you use a flat head screw and the support ring is for the stock plastic servo horn, so I wouldn't bother with it. I'd just try a little blue thread-lock

Fair enough. The only Hitec servo I've ever used was an old 645MG as a replacement for the stock RTR servo in the RC10T4 that was my first hobby-grade RC. Of course back then I though adding a Kimbrough servo saver on top of the servo saver built in the the steering bellcranks was a good idea, so I might have been a little green back then and not really paying attention to what screw size fit the servo