Rear derailleur limit screw stuck - rounded head

ex-pat scot

I'm resurrecting a lovely Campag Record rear mech, but one problem I have is with the recessed limit screws.
One of the screws' head, which is Philips, has rounded so that I can't get any purchase on it with a screwdriver.
I need to loosen this off and replace with new limit screws.

Any idea as to how I might get this screw free?

Pics here
http://www.flickr.com/photos/14610196@N ... 315525429/
The problem one is the H (left one on this picture)

Thanks!

Ben6899

Those screws also take bladed drivers, if you can fit one in and it will hold.

markos1963

If it's stuck as well as rounded I would say it's a drill out job.

keef66

Can you hammer in a torx bit to give enough purchase to unscrew it?

Failing that, and if it's seized a bit, you need to drill a small pilot hole in the middle of the screw head then use the appropriate sized stud extractor to remove it. Very tricky cos you'll need a tiny drill bit and extractor

ride_whenever

Try a regular drill bit but use it in reverse, sometimes works.

JohnnyAllez

Looks to be 4mm screw ? Drill right down the centre at 3.5mm then run a 4mm tap down the hole to clean out the remaining thread from the old screw. Needs accurate work to do properly. If it ends up knackered then 4mm Helicoil will sort it out.

ex-pat scot

Was thinking along those lines.

In the end I managed to get enough purchase on the exposed (threaded) end with a narrow-nosed pair of mole grips, and gradually worked the bolt free until the head was exposed.
Took bloomin ages, but I was reluctant to do the "drilling out" routine until I'd exhaused the non-drill options...

Thanks all