What is a stitching screw?
It's a short self-drilling screw that joins two thin metal sheets together at the point where they overlap. On a roof or cladding run that overlap is the side lap. The screw stitches the two skins tight so the joint doesn't gap or rattle.
What's the difference between sheet-to-sheet and sheet-to-purlin fixings?
Sheet-to-sheet stitching screws hold two metal sheets to each other at the lap. They're short. Sheet-to-purlin (or sheet-to-timber) fixings are longer and hold the sheet down onto the frame below. These stitching screws are the sheet-to-sheet type. Use a longer fixing for the purlin.
What's the maximum thickness these will drill?
1.6mm combined. That's both sheets added together at the lap. Go over that and the No.2 point may struggle to drill through cleanly.
What does the EPDM washer do?
The 16mm EPDM washer is a rubber-bonded washer under the head. As you drive the screw home it compresses and forms a seal around the fixing. That keeps water out of the hole, which matters on an exterior roof or wall.
Do I need to pre-drill?
No. The self-drilling point cuts its own hole through thin steel, so you can drive straight in. Keep the speed between 1,000 and 1,800 RPM and let the point do the work.
What socket do I need to drive them?
An 8mm socket fits the hex head. A nut runner or an impact driver with a socket bit works well.