Lurch,

Thank you for your reply, if not for your sarcasm.

I'll say it again, leave the cement to set then drill,
plug and screw through the box.

I concede that this will work if (a) the head of the screw is larger than
the outside diameter of the plug, or (b) a washer is used. But since
neither of these conditions was mentioned by either of us, it seems to me
that my question was perfectly valid and your tone quite unnecessary. I
thought this group existed for mutual support and advice, not rudeness.

Bert
http://www.bertcoules.co.uk