# Forum Home Renovation Pergolas, Gazebos, Strombellas & Rotundas  Size of hole for m12 bolts

## boggo

Hi all, 
I am slowly constructing the pregola. 
The thing i am wondering about now is how wide the hole has to be to put through M12 bolts. 
The guy at bunnings suggested a 12mm drill bit.  I bought one and have given it a try on a spare bit of wood. 
The bolt goes though easily - even perhaps a little bit to easily and it wiggles around a little bit. 
The bolt will be used to fasten a beam onto a notch in my posts. 
So my question is, should the hole be really tight so that i would need to tap the end with a hammer to go through, or is it fine and normal to have a bit of a wiggle room? 
Cheers 
John

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## paddyjoy

Are you sure it's not an M10 bolt? 
Here is the chart I use as a reference.  technical data from draughtsman.co.uk

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## boggo

hmmm it would seem from that chat that it would be M10... I will check tomorrow.  In any case, for the type of application given, would i need a close fit, medium fit or loose fit?

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## paddyjoy

I would go for the close fit, you can tap it through with a hammer if need be. Also I believe you need to use the cup head bolts that are suitable for external/treated pine Zenith M10 x 150mm Tech-Shield Cup Head Bolt And Nut - 2 Pack

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## sol381

go 1mm higher.. 13mm for 12mm bolt is perfect ...it should never be a tight fit.. you want the 2 pieces of wood to compress together without the bolt  getting stuck in the wood..

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## METRIX

M12 needs a 13mm bit, the bolt should push through and be snug, only use cup head bolts and hit them with a hammer to lock the square bit of the bolt into the timber.
If the bolt wobbles, it's not a M12 you have, probably a M10.

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## intertd6

M12 needs a 12 mm bit, the threads are rolled not cut onto the bolt shaft which isn't 12mm , which is why it may seem loose in the hole.
inter

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## boggo

The Beam is hardwood - the part the cup head would go into.  Would it still be feasible to hammer the cup head into it as hardwood is very hard (f27)?  
BTW My first post went in and seems to have worked out very well indeed.  Nice and straight  and concrete looks good.

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## boggo

So i have one of the Bolts with thr tag still on (BMD0150 ) Zenith and it is an M12. These are just Hex bolts, and it sounds like i might need to return and get cup head ones instead.  But still want to figure out this size thing. 
The drill bit is a Sutton Tools Auger Bit 12.0mm x 270 
and the bolt was loose. 
I will go and try again now and report back

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## boggo

I am sure you all have been glued to the screen in anticipation of the results. 
So I tried again and same thing happened 
Attached are three pictures showing the gap when i put the bolt through so you can see how loose it is, the drill bit i am using, and a measure of the bolt. When i looked at it is was pretty much 12mm, although in the pic it does look a little less than that.  So with the tag on the bolt, the measurment and the fact that i got it out of the 12M bolt bucket at bunnings leads me to be pretty certain that it is a 12M bolt.  Could the type of drill bit make a wider channel through the wood? Does the gap betwene the bolt and wood in the picture  seem loose to you or normal? 
cheers

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## paddyjoy

> the fact that i got it out of the 12M bolt bucket at bunnings leads me to be pretty certain that it is a 12M bolt.

  The M12 bolt bucket at bunnings will contain every bolt size except M12  :Tongue:  
From the picture it looks like it is closer to 10mm than 12mm?

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## intertd6

It looks like it's under 12mm & the thread is cut not rolled into the shaft, you need to measure with a set of vernier's be sure about what measures what. That bolt is only passivated zinc & will start to rust if exposed to the elements 
inter

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## Marc

M12, 12mm drill - M10, 10mm drill. Particularly for pine. Reason is that if the fit is loose, the square bit under the cup head will not have enough grip and will turn when you tighten the nut, bloody frustrating if it happens.

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## phild01

I used to use 12 for 12 but now go slightly more and agree with 12.5-13.  For green timber definitely go larger.

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## boggo

So I typed in the bar code which is on the actual bolt (9310086854468) and when I search google for that is comes up with this Zenith product catalogue and under the bar code it is a 12M bolt.  http://www.itwproline.com.au/Article...logue.pdf.aspx 
However, when i try and measure more closely with my ruler (i have no other measuring equipment), it would appear to me to be about 11mm 
Inter, you said this type of bolt would rust, but it says on the box it was for external use and had a special Tech-Shield Coat as per the link posted above:  Zenith M10 x 150mm Tech-Shield Cup Head Bolt And Nut - 2 Pack

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## phild01

Change the tech shield to gal if treated pine.

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## intertd6

> So I typed in the bar code which is on the actual bolt (9310086854468) and when I search google for that is comes up with this Zenith product catalogue and under the bar code it is a 12M bolt.  http://www.itwproline.com.au/Article...logue.pdf.aspx 
> However, when i try and measure more closely with my ruler (i have no other measuring equipment), it would appear to me to be about 11mm 
> Inter, you said this type of bolt would rust, but it says on the box it was for external use and had a special Tech-Shield Coat as per the link posted above:  Zenith M10 x 150mm Tech-Shield Cup Head Bolt And Nut - 2 Pack

   sorry it looked like it was just passivated zinc but if it's their new coating it's suppose to be 4 times as good as HDG in treated pine.
inter

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## intertd6

> Are you sure it's not an M10 bolt? 
> Here is the chart I use as a reference.  technical data from draughtsman.co.uk

   That table is ideally for metal work.
inter

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## phild01

> sorry it looked like it was just passivated zinc but if it's their new coating it's suppose to be 4 times as good as HDG in treated pine.
> inter

   Originally bought this type of coach screw and pulled them out for gal because of something I read somewhere, just can't recall what it was I read.  Maybe the standards say gal for decks and not tech shield.

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## justonething

For softwood 12mm bit for M12 bolts, for hardwood, 1/2" bit for M12 bolts.

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## PlatypusGardens

"How many renovate forum members does it take to drill a hole"   :Biggrin:

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## PlatypusGardens

> However, when i try and measure more closely with my ruler (i have no other measuring equipment), it would appear to me to be about 11mm

  Lay the bolt on the bench, stand a setsquare either side of it, measure the distance between the squares.  :Wink:   
(or use some right angle steel/ally if you haven't got two squares)

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## Marc

> "How many renovate forum members does it take to drill a hole"

  Ha ha you are right, you would think such a simple matter would bring consensus ... oops, better don't go there.
Just to add my own guess since the OP does not have a caliper. 
Some bolts have the thread cut hot without removing any material. The tool pushes in the steel and the thread comes up raised and so the diameter of the bolt at the thread is larger than the shaft it was cut in. If the thread is cut by turning, metal is removed and the diameter of the bolt is uniform. The earlier method allows to make a 12 mm bolt with a probably 11 mm or 11.5 mm rod. For a wood bolt that is not rated, this is passable from the resistance point of view, but creates a problem with the head square base that when fitted in a 12mm hole, has a reduced amount of timber to grip and stop it from turning. 
A bolt that has the thread cut and not raised when fitted in a 12 mm hole will have not only the additional bit of wod but a bit of friction on the shaft that adds to the force required to keep the bolt from turning.  
As far as the choice of HDG or the new coating, my experience is that HDG does rust in treated pine. I usually lay the bolts in a row on some newspaper and spray paint them with a pressure can to add some additional life to the HDG. I believe the new coating has some zink under the whatever the coat is, and is designed to last longer in TP. I have not seen this improved results myself since this is a new product.

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## METRIX

The Zenith Bolts Bunnings sell are very ordinary quality, the threads are made from slightly undersized stock to save them material, this is quite common for bolts imported from China, and why the nuts wobble on the threads. 
There was a good article from an Australian supplier of "quality" bolts, they showed how your average Imported bolt is around 5 - 7% smaller in diameter than they should be. 
Not sure about the TP treatment effect on the bolts, Tech Shield is an additional coating on top of a HDG bolt, IMO I think it comes down to the quality of the HDG of the original bolt. 
Below are some photos of a dodgy built deck visited last week, you can clearly see all the bolts used are stuffed, but the HDG nails right next to the bolts look almost new, the owner said nobody has added any additional nails since new, so these must be the original nails, and none of them were rusted, so why were the bolts affected so bad and not the nails, cheap rubbish bolts I assume.

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## boggo

Hi Metrix, 
Those pictures are quite telling!  So which manufacturer would you suggest I use for long lasting bolts?

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## PlatypusGardens

> Some bolts have the thread cut hot without removing any material. 
> The tool pushes in the steel and the thread comes up raised and so the diameter of the bolt at the thread is larger than the shaft it was cut in.  
> If the thread is cut by turning, metal is removed and the diameter of the bolt is uniform. 
> The earlier method allows to make a 12 mm bolt with a probably 11 mm or 11.5 mm rod.

  Indeed. 
I have some here actually   
One of each

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## METRIX

> Hi Metrix, 
> Those pictures are quite telling!  So which manufacturer would you suggest I use for long lasting bolts?

  I use online suppliers such as Scrooz, or United, their bolts are higher quality than the green shed ones, and cheaper, but you need to buy in qty, or if you want your fastener to outlast your structure, use Stainless.
If you can find Hobson fasteners these are good quality.

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## METRIX

> Indeed. 
> I have some here actually   
> One of each

  Here is a good video of how their made.  https://www.youtube.com/watch?v=3kxcw08p_oY

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## PlatypusGardens

> Here is a good video of how their made.  https://www.youtube.com/watch?v=3kxcw08p_oY

  
Haha I'll look at that later, othewise I'll be here all morning looking at "how it's made" videos   :Rolleyes:

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## METRIX

> Haha I'll look at that later, othewise I'll be here all morning looking at "how it's made" videos

  The Nails one is interesting as well,   https://www.youtube.com/watch?v=CUTTmtLKD2g

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## Marc

Yes, I have seen plenty of bolts in that condition in the stirrups. Probably a combination of extra moisture at that point of the post, chemicals in the timber and the way galvanising is done on bolts. 
There are a few different methods to achieve HDG. The way the steel is cleaned before it is dunk in zinc is crucial. Large pieces are cleaned with what they call a pickling bath, a mixture of acids. galvanised wire is dunk in moted lead to clean before zink. Nails are galvanised by turning them into what looks like a red hot cement mixer. the nails turn and turn at orange red temperature surrounded by molten zinc. I don't know how the bolts are galvanised but judging from the price they probably get a summary process that is barely adequate. Bolts inside joists and bearers don't look much better than that one in a fully exposed treated pine deck after 10-20 years. I think the added treatment on top of the zinc is a welcomed one. Unfortunately there is no way for us to know the reality in 10 years time. 
Perhaps we could throw a few in a bucket of vinegar or diluted chloridric acid

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## PlatypusGardens

> 

  
Have seen that on many occasions, particularly when pulling down the old square post/rail hardwood fences.
Bolt head and nut intact and rusted down to matchstick size in the middle.   :Smilie:

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## boggo

I had a look at those online shops and they only seem to sell in bulk.  I went down to bunnings again and this time took the bit of wood with hole in to test out different bolts. 
The stainless steel ones (from Zenith still) seemed to fit much better with not much wiggle at all - when i used the same 12mm drill bit.  In fact, I also tried drilling a 11mm hole and they had no chance of fitting. 
So i thought I would try putting the cup head stainless steal in an old offcut of hardwood. 
It drilled fine, but when I went to hammer the cup head into the wood, the wood started to crack as seen in the picture below. When I tried pine it was fine with no splitting at all. 
The bit of hardwood I will be using is f27  240x45 so it will be much bigger than the decking offcut I tried.    However, the last thing I would want to happen is for the beam to split like in the picture below.  So my question is, do I : 
1. Go back to using a hex head and washers with the hardwood
2. Just hammer the cuphead into the big bit of hardwood as it will not split
3. use some type of tool to create the square hole for the cuphead to fit in 
thoughts?

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## PlatypusGardens

A 45mm beam won't split like that. 
But if you're in doubt, go Nut n Bolt.  
Square hole?  :Unsure: 
Come on now.   :Rofl:

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## r3nov8or

Square hole? Mortise chisel!  https://www.machinemart.co.uk/shop/p...mortise-chisel 
Edit: those bits go in machines like this, so, yeah probably beyond the budget here...  :Smilie:   https://www.carbatec.com.au/joinery-...ising-machines

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## METRIX

> I had a look at those online shops and they only seem to sell in bulk.  I went down to bunnings again and this time took the bit of wood with hole in to test out different bolts. 
> The stainless steel ones (from Zenith still) seemed to fit much better with not much wiggle at all - when i used the same 12mm drill bit.  In fact, I also tried drilling a 11mm hole and they had no chance of fitting. 
> So i thought I would try putting the cup head stainless steal in an old offcut of hardwood. 
> It drilled fine, but when I went to hammer the cup head into the wood, the wood started to crack as seen in the picture below. When I tried pine it was fine with no splitting at all. 
> The bit of hardwood I will be using is f27  240x45 so it will be much bigger than the decking offcut I tried.    However, the last thing I would want to happen is for the beam to split like in the picture below.  So my question is, do I : 
> 1. Go back to using a hex head and washers with the hardwood
> 2. Just hammer the cuphead into the big bit of hardwood as it will not split
> 3. use some type of tool to create the square hole for the cuphead to fit in 
> thoughts?

  Of course it will split, the timber is too thin for what your trying to bash into it and the hole is too close to the edge.
Hardwood will split as it is very dense and why it's so strong, Pine is soft, the square bit will just dig into the timber. 
What is it your going to build, and what dimension timbers are yo going to use, if your wanting to bolt close to edge like your pic, do what PP said, get HEX versions of the bolts and give the cuphead the flick.

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## PlatypusGardens

> Square hole? Mortise chisel!  https://www.machinemart.co.uk/shop/p...mortise-chisel

  
Yes yes but you wouldn't......not for cuphead bolts unless you really *really* REALLY _HAD TO._

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## r3nov8or

> Yes yes but you wouldn't......not for cuphead bolts unless you really *really* REALLY _HAD TO._

   Of course. Just saying. Just to keep in mind for when one starts a custom furniture business etc  :Smilie:

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## PlatypusGardens

> Of course. Just saying. Just to keep in mind for when one starts a custom furniture business etc

  
Is one considering starting such a business (or etc) ?

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## boggo

It is for a pergola. 
This will attach a hardwood beam, onto a pine 135mm post.  The Hardwood is 45x240 and the bolts would be not too close to the edge.

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## r3nov8or

> Is one considering starting such a business (or etc) ?

  Dreaming of, yes. Seriously considering, no  :Smilie:

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## Marc

240x45 hardwood for a pergola? Mama ... Do you know it is $40 a meter? if KD even $60 ...

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## PlatypusGardens

> 240x45 hardwood for a pergola? Mama ... Do you know it is $40 a meter? if KD even $60 ...

  
Dang, I just noticed that it said 240 as well.
A bit excessive perhaps? 
big span?

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## r3nov8or

I recall just 2 posts for 5 metre span?

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## boggo

There is just one piece of hardwood in the whole construction... It is a beam with a fairly long span, so I had to go hard wood. Some wood vendors said pine 240x45 would be ok, but other said it had to be hardwood - so i decoided to play it safe and get the bit of hardwood.  It was 300 bucks!  Better not stuff up drilling that one!

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## PlatypusGardens

Hehe fair enuff.   :Smilie:

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## Marc

> The Nails one is interesting as well,   https://www.youtube.com/watch?v=CUTTmtLKD2g

  That is an interesting machine, probably an old method of making nails. I was a fitter at the Australian Wire Mill in Chiswick and we had nail machines among many other and we fed them extruded wire to the right size and it would pull the wire in one side and spit the nails from the other side faster than an Uzi machinegun. None of that cutting rods first and put them in a wheel. We also made "fibrosteel" a russian invention I was told, to reinforce concrete with little tiny rods of steel with both ends split open in a Y pattern, mainly used for dams and bridges... but that is another story.

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## commodorenut

> Lay the bolt on the bench, stand a setsquare either side of it, measure the distance between the squares.   
> (or use some right angle steel/ally if you haven't got two squares)

  Even quicker, and easier, is to wind a shifting spanner (adjustable wrench...) until it nips up against the bolt shank, and measure the gap.
Some shifters even have a scale printed on the jaws for a quick "rough & ready" eyeball measurement.

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## Marc

> There is just one piece of hardwood in the whole construction... It is a beam with a fairly long span, so I had to go hard wood. Some wood vendors said pine 240x45 would be ok, but other said it had to be hardwood - so i decided to play it safe and get the bit of hardwood.  It was 300 bucks!  Better not stuff up drilling that one!

  So that you don't have to drill close to the edge, you can leave a bit of the beam go past the post rather then cutting it flush.

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## PlatypusGardens

> Even quicker, and easier, is to wind a shifting spanner (adjustable wrench...) until it nips up against the bolt shank, and measure the gap.
> Some shifters even have a scale printed on the jaws for a quick "rough & ready" eyeball measurement.

  Amazing. 
All the time I spend measuring, levelling, squaring, truing, lining stuff up, clamping stuff together, centering, dividing in to thirds, and so on, that is one thing that's never crossed my mind   :Unsure:  
Sometimes the most obvious solution is the one you never think of haha.
good one.   :Smilie:

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## PlatypusGardens

Ok we're making a big issue out of something simple here...  
Boggo - is there somewher other than Bunnings/Masters to buy bolts near you?
Total/Global/United Fasteners or some place like that?
Bearing/Hydraulic shop?
Engineering shop? 
Take your piece of pre-drilled board in, or the drill bit you're using, get yourself some nice stainless hex head bolts and nuts and washers.
Most places will sell you small quantities, and you'll get the right bolt for the job. 
I'm guessing since it's a single span you only need 4?    :Smilie:

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