# Forum Home Renovation Fences & Screens  screws to use on joining mod wood to steel post

## chunky59

Hi all 
I am building a slated screen at the rear of my yard 
I have installed 75 x 75 gal tube posts at about 1100 mm centres.  I want to attach some 68 x 17 mm modwood boards to them 
In their spec sheets they sujjest to use Tek screws to attach them to the posts. 
However i think the head of the Tek screw will be too big and stand out when you look at the screen from the deck 
Does any body know if i can use and a countersunk headed screw to attach the baords to the post so the screws do not stand out as much? 
Would i be best to use S/S scews also or would Gal be OK?  I was thinking of painting all the heads once fitted so they blend in more anyway. 
any help would be appreciated 
Chunky59

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## OptoIso

I have done a similar project, but using 19mm thick merbau slates, fixing to 2mm steel frame.
I used regular S/S 8G screws, with mixed results.
Some of the boards are now loose after a year, I think due to the pilot hole in the steel being two big and the harder frame just burring up the S/S screws.
I am toying with the idea of stepping upto 10G screws, as the threads may be coarser. 
I think the key it to find a Screw which has threads (TPI) larger than the thickness of metal your fixing two, so the screw isnt trying to cut its own thread into the metal.
Tek screws would be too large and ugly. Experimentation is the key with things like this.

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## SilentButDeadly

Try BuildexÂ®. One of the worlds leading manufacturers and suppliers of self-drilling screws and fasteners. There's plenty of chocie there.

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## chunky59

Thanks for that 
How do you determine the length of screw to use, is there some time of formula. like timber thickness plus 10 or 20 mm 
I am thinking of using a metal tek countersunk head screw.  I will pre drill the mod wood, do i need to pre-drill a pilot hole in the metal post? 
Chunky59

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## SilentButDeadly

> Thanks for that 
> How do you determine the length of screw to use, is there some time of formula. like timber thickness plus 10 or 20 mm 
> I am thinking of using a metal tek countersunk head screw.  I will pre drill the mod wood, do i need to pre-drill a pilot hole in the metal post? 
> Chunky59

  Long enough to fully engage the thread with the steel so at least 10mm than timber thickness.  Tek screw should self drill through the mild steel no worries...

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## chunky59

Thanksfor that i will try on the weekend with some 40 mm long tek screws

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## barney118

10-16 x 33mm Wafer Head Square Drive Self Drilling Screws Qty: 100 Stainless | eBay, I used these to attach decking boards to my sliding gate steel angle.

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## ScroozAdmin

> 10-16 x 33mm Wafer Head Square Drive Self Drilling Screws Qty: 100 Stainless | eBay, I used these to attach decking boards to my sliding gate steel angle.

  You just need to be aware that grade 410 stainless fasteners like these, despite the name, are not very corrosion resistant, it's just about the lowest grade alloy with lots of carbon steel steel in it, so it can rust. It's a cheap way of making self drillers and selling them as stainless. Better quality ones in 304 or 316 grade have a hardened steel drill point welded to the stainless body but the process makes them a bit pricey. You'd be better off with galv rather than 410 tbh.

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## METRIX

When we do screens they are usually part of a deck so the same screw is required for aesthetics. 
The way we get around it is, to put a piece of timber inside the entire length of the post, make it a snug fit but not too tight or it will get jammed and will be very difficult to get it back out to trim it. 
Put your board on and pre drill the timber and the steel post with a pilot hole (this is to keep the hole in the timber small) if you use a set of small quick grips and spacers you can drill all the holes required for one board. 
Then remove the board and drill the post with a larger hole which will allow the screw to pass through without binding on the steel post, if you are using stainless steel screws these will either break or strip the treads off if they bind on the wall of the posts, put the board back up just screw in your choice of screw into the timber which is inside the post, works a treat but does take a little longer to do but keeps the look consistent if that is what's required.

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## jimj

Very Nice--Great idea-method&advice 
jimj  restore-a-deck.com.au :Biggrin:

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