Housemartin wrote

Try using the new screw in bolts not sure what screw fix calls them but
they work really well and are very reliable.

Would they be the Multi Monti http://tinyurl.com/all9f ? I've often
wondered about them.

BTW it claims they are great in cracked and uncracked concrete - what on
earth is that? Is it just as it seems - concrete that has cracked?

Dave