Frank Stacey wrote:
I want to remove a bolt which takes a 4mm hex alan key - well it's not quite
that simple. The hex hole has a central pin which prevents the insertion of
a standard alan key. It may be a useful security feature but nobody knows
the wherabouts of a suitable key so it's a problem.

Ayone know if suitable alan keys can be obtained anywhere? I can't find
such things via screwfix.

I'm pretty sure you'll find one of those in this kit:
http://tinyurl.com/lmzp2 or
http://www.screwfix.com/app/sfd/cat/pro.jsp?cId=100193&ts=15968&id=18983#

David