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.

In some cases, just the right size of flat screwdriver can work.
In other cases, it breaks the pin off, and you can use a conventional
key.