What diameter pilot hole for 5mm diameter SS screw?

[markharro]

Anyone have any advice on this? Need to drive 100mm stainless steel screw through softwood battens then into roof rafters. Guessing it may be best to pilot hole first?

[Mr Punter]

I would do clearance holes through the battens - maybe 5mm so you can load the screws.  Assuming you have lots to drill, you could stack the battens and do 3 at a time.  Once you have set one up you can use this as a template.  If screwing into the rafter without a pilot is tricky you could do a 4mm pilot but not full depth.

[JohnMo]

Buy self drilling screws?

[Temp]

https://www.diydata.com/carpentry/screw-holes/wood-screw-holes.php

 

Says..

 

Pilot 2.0 or 2.4 (softwood) 2.8mm (hardwood).

 

As they are SS I would go on the larger side. Perhaps even 3mm.