# Counterbores for UNF 10-32 Socket Cap Screw



## MCB (27 Jun 2016)

Can anybody suggest, please, where I might obtain a counterbore for a 10-32tpi UNF Socket Cap Screw.

(it's 5.0 mm pilot and 8.0 mm or 8.5 mm clearance for the cap)

I need to use one in a project where I have to open several holes this size.

All my normal sources only sell Metric Counterbores (if any) but I know that there are lots of very helpful people who read this List - hence this request for help

With best wishes and thanks. 

MC


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## DTR (27 Jun 2016)

I'm too cheap to buy counterbores, I've always used an appropriately-sized slot drill instead. Would that be a viable alternative? 

Incidentally, all the counterbores I've either seen either online or in the flesh have been unnecessarily long, and I don't think my drill or mill have enough headroom to make them practical. Slot drills are conveniently short.

edit: just looked online again, I was wrong about there being no such thing as a short counterbore


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## MCB (27 Jun 2016)

DTR":2hcc0amk said:


> I'm too cheap to buy counterbores, I've always used an appropriately-sized slot drill instead. Would that be a viable alternative?
> 
> Incidentally, all the counterbores I've either seen either online or in the flesh have been unnecessarily long, and I don't think my drill or mill have enough headroom to make them practical. Slot drills are conveniently short.
> 
> edit: just looked online again, I was wrong about there being no such thing as a short counterbore



Thank you for taking the time to respond.

That would be a good suggestion ................ if I had any slot drills!

I was thinking of drilling on my lathe; I would hope that would give more accuracy

Have you found a supplier of SHORT Counterbores for 10-32 UNF?

With best wishes and thanks. 


MC


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## woodpig (27 Jun 2016)

It's true that metric counterbores are more commonly available over here but you can still use them for imperial screws if the size is suitable. You can always drill out the through hole a bit larger if needed. From experience imperial counterbores often seem over sized to my eye and look ugly. I've used bullet drills and milling cutters to counterbore followed by the correct size drill bit for the bolt. Things get a bit more difficult for existing holes though, you may have to source the correct tool from somewhere like the US if you can't get one over here. I have several counterbores and none of them are particularly long.


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## CHJ (27 Jun 2016)

Take a spare standard twist drill and grind a guide spigot on the end with a flat or very near flat cutting shoulder.


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