What screws to use.

skye16 · 15 Jul 2018

Hi
I want screw a piece of wood to a metal strip. The wood is 20mm thick. The metal strip is about 2 or 3mm thick. I can't get behind the metal strip, to use nuts and bolts. The gap behind the metal strip is about 15mm.
Please could you tell me what sort of screws I should be using? It would be better if they were rustproof.
Thanks.

rsgaz · 15 Jul 2018

For 'rustproof', they need to be stainless, zinc plated (BZP) only last so long outside.

If you drill the right size pilot, any normal self-tapping stainless screws will work.

"Self drilling" screws are available, but not sold in as many head types/lengths/finishes/etc, so might be impossible to find exact ones to suit your dimensions.

If it needs to be very strong also, then drilling and tapping the hole first is the best option IMHO(without going overboard with rivnuts, etc). That way you are then free to use whatever machine screws you like in terms of head style, etc.

foxhole · 15 Jul 2018

skye16 said:
Hi
I want screw a piece of wood to a metal strip. The wood is 20mm thick. The metal strip is about 2 or 3mm thick. I can't get behind the metal strip, to use nuts and bolts. The gap behind the metal strip is about 15mm.
Please could you tell me what sort of screws I should be using? It would be better if they were rustproof.
Thanks.

Would be more helpful to tell us what you are trying to achieve.?

endecotp · 15 Jul 2018

https://www.screwfix.com/p/easydrive-countersunk-head-self-tapping-screws-8ga-x-1-100-pack/7496h

skye16 · 16 Jul 2018

Thanks for the advice on self tapping screws. I had never heard of them before. And thanks for the Screwfix link.
I only need half a dozen screws. Can you tell me what drill bit size I would need for drilling a hole in the metal, if I get no. 8 screws?
Thanks

rsgaz · 16 Jul 2018

skye16 said:
what drill bit size I would need for drilling a hole in the metal

What metal is it?

skye16 · 16 Jul 2018

I'm not sure. I think it is just painted steel. Does it make a difference?

rsgaz · 16 Jul 2018

Use a 3.5mm HSS drill then. If it was something softer like aluminium, I would have said 3.0mm.

skye16 · 16 Jul 2018

I suppose what I was thinking is it a smaller hole that the screw size, or is it a size 8 drill bit, for the self tapping no. 8 screw?
Thanks.

skye16 · 16 Jul 2018

Thanks rsgaz. I think I posted just as you did. I'll see if I can get a small amount of screws and drill bit from ebay.

rsgaz · 16 Jul 2018

skye16 said:
is it a smaller hole that the screw size

Yes, a number 8 screw has a nominal size of 4.17mm, but they usually measure about 4.05 to 4.10.

^woody^ · 16 Jul 2018

skye16 said:
I'm not sure. I think it is just painted steel. Does it make a difference?

You wont need rust-proof screws if drilling into ferrous metal.

Roger928 · 18 Jul 2018

^woody^ said:
You wont need rust-proof screws if drilling into ferrous metal

So a screw driven into an aluminum roof will never rust?

^woody^ · 18 Jul 2018

Roger928 said:
So a screw driven into an aluminum roof will never rust?

Does this hypothetical screw contain iron, and is this hypothetical roof on Mars?

Roger928 · 18 Jul 2018

^woody^ said:
Does this hypothetical screw contain iron, and is this hypothetical roof on Mars?

Roof is on earth. Screw contains metal.
You say it won't rust? I say it will.

diynot

If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.

Select the supplier or trade you require, enter your location to begin your search.

Are you a trade or supplier? You can create your listing free at DIYnot Local

What screws to use.

Similar threads