Metric thread dimensions

Could someone please confirm if I've right here:
A 2mm[1] wide slot would accomodate an M2.5 threaded bar; A 4mm[2] wide slot would accomodate an M5 threaded bar?
[1] A 2mm HSS drill shank sit shappily in the slot - a 2.5mm dill will not.
[2] A 4mm drill shank sits in the slot.
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Why?
It's that screed floor that has a crack down the middle (builder cock up[3]). I have decided to angle grind 30cm long slots perpendicular to the crack acorss the crack at 30cm intervals.
I will then resin A2 stainless threaded bar into these slots using Uzin KR416[4]:
http://www.pwflooring.co.uk/subfloor-preparation/preparation-and-repairs/uzin-kr-416.html
My wall chaser cuts slots with 2mm drill shank clearance, and I can acheive a 4mm slot if I clamp the two diamond discs onto each other[5].
So I'm deciding what size bar to buy...
Cheers,
Tim
[3] Don't get me started on builders. Every bloody time I have to fix something... And I trust me more, so no, not calling them back... Too much hassle.
[4] It's a low viscosity resin designed for the job with screed penetrating characteristics.
[5] Seems dodgey but a test run indicates the chaser is not unhappy. I'm well protected by shielding so the risk is low.
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Tim Watts wrote:

Neither statement is correct 2mm slot needs M2 thread to fit in it 4mm slot needs M4 thread to fit in it
The core diameter of M2 thread will be 1.6mm - bu88er all strength Core of M4 is 3.3mm and so 4 x the cross sectional area of the M2
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On Sunday 19 January 2014 19:49 Bob Minchin wrote in uk.d-i-y:

Thanks John.
In that case I must have misunderstood this:
http://www.tribology-abc.com/calculators/metric-iso.htm
- it said M2.5 needs a drill diameter of 2.05mm. Is that because a 2.05mm shank drill actually drills a 2.5mm hole?
In that case, i shall have to double up my discs and use M4.
M2 threaded bar is not readily available and is probable too thin.
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On 19/01/2014 20:12, Tim Watts wrote:

Those are tapping drill sizes - the hole you drill when you want to cut that thread in some material. A clearance drill is needed to give a hole that the thread will enter freely. This gives both tapping and clearance drill sizes:
http://www.engineeringtoolbox.com/metric-threads-d_777.html
Colin Bignell
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On Sunday 19 January 2014 20:18 Nightjar wrote in uk.d-i-y:

Thank you sir! That is a much better table than the one I found... And I get the point about tapping vs clearance - but it was not clear form my initial googling....
http://www.metals4u.co.uk/ seem to have the best prices for metre lengths of A2 threaded bar.
Here's what I'll cutting and dropping the bar into:
http://www.flickr.com/photos/timjwatts/12037285193/ http://www.flickr.com/photos/timjwatts/12037025135/
BTW - the bright light in the background is one of these:
http://www.toolstation.com/shop/L/s/n/d220/sd2480/p45540
I'm very impressed - LED and rechargeable. I really got it for the wiring work in the roof space - cold running and shock proof were the main things.
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Tim Watts Personal Blog: http://squiddy.blog.dionic.net/

http://www.sensorly.com/ Crowd mapping of 2G/3G/4G mobile signal
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On 19/01/2014 20:12, Tim Watts wrote:

No, that's the size of drill you need if you want a hole ready for tapping to M2.5
The 2.05 is the minor diameter of the thread (i.e. if you measure the internal diameter of a M2.5 nut, that is what you will measure), but the major diameter (i.e. the diameter of the bolt) is 2.5mm
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Cheers,

John.
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On Sunday 19 January 2014 20:27 John Rumm wrote in uk.d-i-y:

OK - all clear now :) - Ta muchly! Glad I asked - PITA mistake that would have been!
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I'd assume that was the start hole for tapping a thread. Clearince would be the same size as the bolt plus a little more for comfort.

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On Sunday 19 January 2014 19:49 Bob Minchin wrote in uk.d-i-y:

I agree that M2 is getting rather too weedy - as I replied to John, I shall chance doubling up my wall chaser discs to cut an M4 capable slot.
I never got the hang of screw dimensions (any any format!).
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On 19/01/2014 18:41, Tim Watts wrote:

Seems unlikely, unless I have missed something. The outer diameter of the metric thread is the size specified. So M5 bar will have a 5mm outer diameter (the minor diameter will be near enough 4mm - but that is not going to help getting it into a slot!)
--
Cheers,

John.
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