Also.If theres a bit sticking out then have you tried tightly locking a pair of mole grips onto the stump and attempting to turn that
NOTE- To everyone
Not everyone has a milling machine or pillar drill or any fixed engineering machine.Most will have a drill and the ability to buy a drill bit of the correct diameter
The pound shop and the like has little kits of 3-5 different sizes of screw extractor.
Drill a hole if you can in near enough the centre of the stuck bolt.
Chances are you dont own a hardened centre punch so use a wood nail though a masonry nail is better because that is hardened.
Drill about 5mm into the top and then attempt to screw in the extractor.Ive found that they bite in quite quickly and because its a reverse thread the harder you force it in the better as this also forces it to undo.
Ive taken out bolts at the bike station that have been rusted in for a good 30 years[judge from the age of the bikes]
If you own a drill then your outlay should be no more than a fiver for the drill bit and extractor kit
Still waiting to hear which model they are though
1976 Raleigh Chipper,1991 Muddy Fox Adventurer, 1992 Raleigh Diablo ,1992 Rudy Project, 1995 Cannondale M200 ,1997 Santa Cruz Tazmon ,1997 Specialized Stumpjumper ,1997 Specialized Rockhopper ,1997 Marin Quake 9.0,1998 Marin Pallisade trail ,1998 Raleigh Torus,1999 Orange Clockwork , 2005 Kona Hahanna , 2010 Orange Pure7
The Marvellous Mechanical Hope Collection