You could try hammering in the next size up allen key into the remnants of the fastener.
Or, get a left-hand drill bit, and try to drill the head off. Quite often the vibration / heat is enough to get the fastener moving.
Sometimes trying to tighten up the fastener, before loosening it helps.
Loads of on-line parts fiche, like this here: https://www.motorcyclespareparts.eu/en/yamaha-parts/2016-xsr700-motorcycles/frame I'm guessing that this is the part you're after https://www.partspak.com/productcar...00-Bolt-Hexagon-Sock-901100811100-p557928.htm
I often replace fasteners with the equivalent in stainless steel. Care is needed if the fastener goes into a stainless steel item, or is load bearing, eg brake calipers, engine mounts.
Or, get a left-hand drill bit, and try to drill the head off. Quite often the vibration / heat is enough to get the fastener moving.
Sometimes trying to tighten up the fastener, before loosening it helps.
Loads of on-line parts fiche, like this here: https://www.motorcyclespareparts.eu/en/yamaha-parts/2016-xsr700-motorcycles/frame I'm guessing that this is the part you're after https://www.partspak.com/productcar...00-Bolt-Hexagon-Sock-901100811100-p557928.htm
I often replace fasteners with the equivalent in stainless steel. Care is needed if the fastener goes into a stainless steel item, or is load bearing, eg brake calipers, engine mounts.