I have some lengths of 50mm x 25mm x 1.5mm thick seam welded steel box
left over from when I built the garage doors.

Well, I've got a quote of 40 quid for enough 3/4" x 3/4" 16 gauge to span 3
times. That, I believe means 19mm x 19mm @ 1.5mm thick. Hopefully, this will
be stiff enough to stop the Granite cracking. It also gives me space for a
5mm MDF sheet over the top, which should make the worktop fitting a bit
easier. I will measure again carefully, in case I can fit the 1" stuff in.

Christian.