Metric Drill Bit Sizes

Randy Lucius

Well-Known Member
Looking at some 6mm and 8mm pins. 6mm=.236 a #73 bit is .240
8mm is .314 a #67 is .320. The #73 looks like it will be fine not sure about the #67.
What do you guys use or recommend?
 

52 Ford

Well-Known Member
You can always ream after drilling.

It's worth noting that twist drills are not super precise. If you have a drill that measures, for example, 0.500", it may drill a little under or over sized. This can be due to a lot of things, like how it's sharpened (uneven flutes can cause an oversize hole), chuck runout, etc. Heck, even things like what kind of cutting oil you use effect bore diameter. If I'm not mistaken, thick cutting oil can cause a slightly oversized hole (compared to something thin like IPA or water-based cutting fluid).

If you're concerned with consistency, I'd pick up some readers. You can get them in pretty much any size imaginable.

Sent from my Champion Forge using Tapatalk
 

Randy Lucius

Well-Known Member
You can always ream after drilling.

It's worth noting that twist drills are not super precise. If you have a drill that measures, for example, 0.500", it may drill a little under or over sized. This can be due to a lot of things, like how it's sharpened (uneven flutes can cause an oversize hole), chuck runout, etc. Heck, even things like what kind of cutting oil you use effect bore diameter. If I'm not mistaken, thick cutting oil can cause a slightly oversized hole (compared to something thin like IPA or water-based cutting fluid).

If you're concerned with consistency, I'd pick up some readers. You can get them in pretty much any size imaginable.

Sent from my Champion Forge using Tapatalk
Thanks. Really good information! I use a #30 on 1/8 pins and a "F" on 1/4 pins and they fit great. Just trying to get the same fit with metric pins. Out of curiosity I just measured a 6mm pin. Should be .236 and it measures .232. That's an .008 difference with a #73 bit. Might just need to get a few bits on either side and see which works the best. Thanks for the response everybody!
 
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