This was a topic I raised about a month ago and there was a suggestion
of an item from the Axminster catalogue.

http://www.axminster.co.uk/default.asp?part=AW635R

I was ordering from Axminster anyway so it was easy enought to add
this in. I was a bit thrown when it arrived as it's a 150mm length of
6mm threaded rod with a knurled nut with a groove machined in it.
It's taken me a month to find out that it is a very basic but simple
solution to the problem - part of that month was finding quite where I
had put the side fence ! OK senior moment.

I've got one of the B&Q 1200W router's and it has, presumably like the
m/c this device is designed for, a 6mm threaded hole in the base
plate. Threaded rod goes into this hole - the side fence has slot in
it which fits into the groove in the knurled nut and hey presto. It's
not as nifty as the fancy ones but for £6 it'll do. There's no
calibration but the thread is M6 x 1 so some marks can be added to the
nut so that one turn is 1mm, etc.

Rob