I have a backplate for a spinner and I need to drill it out to 10mm. What number drill bit does it take for a 8mm and 10mm hole? Can you purchase metric drill bits?
Larry

If its plastic, composite or aluminum you can use an old metric prop reamer.
More accurate than a drill bit unless its had the end turned down or you have a good jig.

Ed M.

Thanks Ed, the backplate is aluminum but all my prop reamers are like new and I hate to ruin one reaming out aluminum.
Larry

If the reamer is hardened and you go slow you should not harm it.

Ed M.

hardneed steel against aluminum.. Al will loose!

If you ream out your back plate with a reamer, I doubt you will ruin it. Gum it up maybe, but not ruin it.. Use a bit of 'cutting fluid' while you 'ream', Use a squirt of WD-40

And yes, you can buy metric drill bits..
8mm = 0.314" or 5/16" (0.3125)
10mm = .3937 or 25/64" (0.390625)

dr,,,,,,,thanks, exactly what I wanted to know. Larry

Try using one of those "step" drills.
They will take out material slowly and the hole will be round

You should really use a reamer for that kind of job. You don't want that hole being opened up off center or you will be out of balance, not good. Drill bits will normally cut off center without a precise setup jig.

Joe, exactly what I did and it didn't seem to hurt the edge on the reamer. You guys are right, I believe using a drill bit would cause more problems then it is worth. It is slower going but the results are worth it. Larry