On Wed, 16 Jan 2019 12:15:00 +0000, Andy Burns
wrote:

Tricky Dicky wrote:

I found out to my cost when trying to install boxes that only
accommodate PB up to 12mm. You can get boxes that will fit thicker PB
and that is probably what you need to specify when ordering.

These claim up to 18mm

https://cpc.farnell.com/pro-elec/19679d/double-dry-lining-box/dp/PL04304?st=dry%20lining%20boxes

Thanks. I make the thickness 18mm but that is not an accurate
measurement given I have not removed the existing box.

There is plenty of space behind so I wonder if a 47mm box would be a
better bet.

Looking elsewhere, I wonder if a pattress box - with four screws in
the corners - would be an option. This must happen all the time with
chipboard. I am amazed that the boxes don't fit by default.