Which drill bit to use.

The greenhouse manufacturer provided 2" wood screws and rawl plugs which required a 7mm bit, so that is what I've used. I borrowed a SDS hammer drill with what I was told was an all purpose bit. This went through the metal flange into the 2' x 3' x 2" concrete flags with no bother at all. Although the galvanised screws have larger heads than the 7mm hole I think I'll get some washers under them to spread the load.

Thank you to all the good folk who have given me advice here on uk.d-i-y. I an well pleased with my greenhouse, now that it's up.

Don

Then how do you get the plug through the smaller hole?

You can say that again! In the gales back in 1987 (iirc) my mother's greenhouse took off, flew over a 6' high hedge and ended up in a field. I still have some bits of aluminium from it.

My parents live up in the cabbage-belt of West Lancs. I think their local record for a flying greenhouse is about 1/4 mile. If a polytunnel takes off, they land somewhere in the Irish sea.