by 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!