A couple of years ago I tightened the bolt attaching my rear mudguard/fender to the eyelet at the hub and it snapped, leaving a 5mm long section of bolt stuck in the thread. Since then I've tried various things to get it out, all ending in dismal failure. So I've had to use the less effective type of mudguards that are strapped to the stays with cable ties.
Getting at the small amount of protruding metal with small pliers: not enough metal to grip it
using a threaded bolt extractor of this type: there wasn't enough thread exposed on the other for the extractor to get a grip
Trying to drill into the middle of the bolt: the drill bit broke!
Any ideas appreciated!
The frame is aluminium. The bike is audax/sportive type.
Update: I tried everything suggested, except the blowtorch, to no avail. So I gave up and got a new frame, something I 'd been thinking of doing for a while as it has been showing its age.