What size pilot hole?

[ben100]

I'm attaching a bath panel & have got some 4mm screws, what size drill bit for the pilot hole should I use for the plastic panel?

 

[mattylad]

The plastic panel I would expect to have a clearance hole, your not screwing into that but through it.
What is behind the panel that you are screwing into?

 

[ben100]

The plastic panel I would expect to have a clearance hole, your not screwing into that but through it.
What is behind the panel that you are screwing into?

I've got the plastic panel & at the bottom behind it I've put a piece of timber which it will screw into.

 

[johnny2007]

4mm.