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Sizing for screws

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Sizing for screws

Postby tabs » 09 Nov 2018, 11:59

Is there a general rule of thumb for this? For example when connecting two different pieces of wood together to determine what gauge and length of screw to use and how many?

I thought I'd ask so in future I can work it out myself. At the moment I'm putting 19m OSB(8x4) onto my roof, screwing through into 6x2 rafters at 400mm centres. I was thinking screwing every 12 inches but really have no idea of the gauge or length of screws I should use.
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Re: Sizing for screws

Postby StevieB » 09 Nov 2018, 13:14

My 'go to' screw is typically a 4 x 40mm. I will go up to 5 x 40 or 5 x 50 depending on the weight or size of something I am trying to fix. For me, this just feels right - nothing scientific to back it up though!

I tend to want approx 2/3rds of the screw into the backing material, so for 18m OSB I would be looking for a 50mm length screw. Distance between them would be close enough to prevent bowing of the board between screws but not so close that you cannot see any effect of putting in an extra screw. So on a 1200mm edge of a board, I would probably do one on each corner, one in the middle, then 1 between the each corner and middle - so 5 screws at approx 300mm intervals. Double up for the long side.

When I was laying ply as a sub base for lino in a bathroom, the recommendation was to screw in a 10cm grid patter across the entire board, which seemed massive overkill to me, so I might be a bit on the frugal side with screws!
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Re: Sizing for screws

Postby tabs » 09 Nov 2018, 13:17

Cheers, i was thinking 40mm plasterboard screws but would rather be on the safe side so will go upto at least 50mm
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Re: Sizing for screws

Postby Robert » 09 Nov 2018, 14:20

I used 45mm drywall screws when I put 18mm OSB on my workshop roof this summer.

I like drywall screws. Reasonable price and pretty rust resistant. Shallow head means you can get away with not countersinking some of the time.

As to spacing about 300 to 400 mm apart. No reason other than what looks about right :)
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Re: Sizing for screws

Postby Mike G » 09 Nov 2018, 16:14

I typically look for 30mm into the batten/ rafter/ stud/ joist, so with 18mm OSB I'd be using a 50mm screw.
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Re: Sizing for screws

Postby RogerS » 12 Nov 2018, 14:04

Anything to do construction-wise I use 5mm screws. Also the Torx head...Pozidrives are so last year.

But while I still have the Paslode then that gets a lot of use !
If opportunity doesn't knock, build a door.
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Re: Sizing for screws

Postby Malc2098 » 12 Nov 2018, 17:28

I'm converted to Torx, too.

Roger, we are so MoneySupermarket...., oh no, that's Skelator!
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