Thread Sizes

What is the thread size for the small screws that are used to hold the key strips down On the 400/500 series registers? What I want to do is tap holes in an aluminum bar for the common register screw sizes so that I can have a better way to hold them when I polish. I read that 6-32, 8-32 and 10-24 are the most common l, just not sure about the really small ones. Has anyone else tried something similar or have a better method for polishing those tiny screws? I am just worried if I try to hold onto the with pliers or something I will end up loosing them. Thanks all

If you use a buffer to polish, be careful, it might unscrew.
 

I use needle nose vice grips I get the pliers very tight. I have not lost one yet. (So far) just don't put a lot of pressure on the wheel and keep on checking on them. Good luck. 

The screw size is a 3-56
Go to McMaster Carr web site and type in this number
5232A55. It is a pin vise that opens from .010 - .312 and it cost about $24.00 plus shipping. I have tried various ways and pin vises and I found this to work the best, It won't mess up the threads. Easy to us

Thanks everyone for the input!

I use a steel plate set up much like you are talking about making. I agree you have to be careful, as sometimes the buffer rotates them and can screw them out.
My plates has enough holes for a complete machine, so I can load it up and do it one time. I leave them in the plate to clean them then spray them with lacquer. Works pretty well.