# Help - drill sizes suitable for Metric taps



## Sportique (20 Jan 2010)

Help.

Please can anyone tell me the correct size of drill bits suitable for taping metric threads into ally or brass.

I have the taps, but I am unsure what drill bit sizes to use.

For example to tap M4, M5, M6, M8 and M10 threads.

Many thanks

Dave


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## xy mosian (20 Jan 2010)

This might help,

http://www.gewinde-normen.de/en/iso-coarse-thread.html

I assume the tapping drill sizes are for steel, perhaps not strictly accurate, but will give you some idea.

xy


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## Aled Dafis (20 Jan 2010)

Sportique

M4 - 3.3mm
M5 - 4.2mm
M6 - 5mm
M8 - 6.8mm
M10 - 8.5mm
M12 - 10.2mm

All from memory, not bad eh?? These are the tapping drill sizes for "Metric Coarse" threads, which are by far the most common, there is a range of "Metric Fine" threads, but they're quite rare in general day to day use, they only get used for specialised purposes.

In fact I get asked about a million times a day in school "what size drill for a ... tap?" My usual answer is "go find out", but they always come back to check, just for reassurance.

Cheers

Aled


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## 9fingers (20 Jan 2010)

For metric or US threads that are based on 60 degree angles, Simply subtract the pitch from the overall diameter.
In most cases the pitch is written on the tap.

Bob


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## Sportique (20 Jan 2010)

OK guys - thanks for all the replies, it is now very clear.

Assistance and advice is always so readily available on UKW. Thanks agaian.

Dave


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## slimshady (20 Jan 2010)

Tapping drill size is easy to remember; it's the M# size minus the pitch.
ie, M6x1.0 = 6-1 = 5.0 , M10x1.5 = 10-1.5 = 8.5
all of my taps have the full metric identifier; M6x1.0 or such-like.
It's just then getting hold of that size drill or the nearest imperial eqiuvalent.
Other option is a Zeus book listing everything, which I have misplaced again. I've got 3 in very secure unknown places.

Slimshady


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## slimshady (20 Jan 2010)

Either I'm a bit tipsy, or I'm a slow typist.
I didn't realise that it took sooo long to write a message.

Slimshady


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## ondablade (20 Jan 2010)

I've always used the dia minus the stated pitch rule too....


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## OldWood (20 Jan 2010)

Sportique
I don't want to sound as if I'm a smarty pants, but you could have got an immediate answer by searching google with something like "metric tap drill" - I'm sure the first out of 900,000 hits would have given you the answer you wanted within 1 minute.

I actually had to do this very search a couple of days ago and the time taken didn't inhibit the project flow at all. I've got printed tables somewhere but the internet was quicker than hunting them out.

Rob


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## dannykaye (21 Jan 2010)

you might find a copy of Zeus worth getting

http://www.axminster.co.uk/product-Zeus-Precision-Charts-Ltd-Zeus-Reference-Book-20633.htm


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## Digit (21 Jan 2010)

Zeus! King of the Gods and the engineer's Bible.

Roy.


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## woodbloke (21 Jan 2010)

Digit":2qy4fh81 said:


> Zeus! King of the Gods and the engineer's Bible.
> 
> Roy.


That dates you Roy, :lol: same as me. I always had to have one to hand or in the top tray of the toolbox when I were a 'prentice - Rob


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## newt (21 Jan 2010)

No one should be without a Zeus, seriously.


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## Digit (21 Jan 2010)

> That dates you Roy,


 
Blast! :lol: When I started I was given a list of essential tools that I was supposed to acquire, (on apprentices wages!), top of the list was a Zeus. 
I was lucky, I lived in an area where a charity gave a bursary to new boys. Bought my first motor bike! :lol: 

Roy.


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## woodbloke (21 Jan 2010)

newt":24371i7v said:


> No one should be without a Zeus, seriously.


Zeus rules...or used to :wink:  - Rob


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## Charlotte (21 Jan 2010)

perhaps that's why my VWs were always rattly old nails. I always used 4mm for M4 and so on.


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## Sportique (21 Jan 2010)

Rob (OldWood) - yes you are right. My humble apologies for wasting the forum' time.

Thanks to everyone for their comments - Zeus is probably an over-kill for my needs at the moment, but thanks.

Dave


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## Digit (21 Jan 2010)

A Zeus gives more info than just tapping drill sizes, it's invaluable for example if you need to know the nearest metric drill to an imperial and vice versa. Can save you buying an awful lot of drills!

Roy.


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