Are freehubs different (apart from obvious Campag/Shimano type differences) If I have a 10 speed Shimano set up, will any replacement freehub do, or do different makes have different fittings? How do I tell what sort of freehub I have?
They're all different. Which hub do you have?
It's off a Calibre Dune, the only information I have is that the hub is a KT 12mm x 197.
Have you tried contacting Go Outdoors or Calibre bikes? Annoyingly, some manufacturers can be very guarded about information for what should be a readily available part. Googling reveals that KT is a sister-brand of Quando - renown seller of cheapo OEM hubs.
If it’s a proper ‘fat’ rear end (197 is) then 100% that isn’t a Shimano hub, so unless the hub mfr has risked legals from Shimano, the Shimano FH’s won’t fit.
It’s annoying when manufacturers who use rebranded hubs won’t come clean what they’ve used or offer spares. Try the ‘UK Fatbike’ group on FB, lots of Dune owners there who may know what Calibre have used from experience...