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Just stumbled across these. Steel rigids, 410mm long, clears a 26+ tyre with guards(!), 650b plus without, boost thru-axle! And you can get them in offsets up to 60mm.
God knows what the full bike looks like.
Could be perfect for some weird monster cross build. I may throw some on my Arkose...

Sheldon's looked like this. Monster, certainly.

Thats the nomad mk3 fork isn't it?
Not monstercross, but rough road expedition touring. What us RSF desendants would be riding, if mountain bikes hadn't been invented.
Doesn't look like they make a boost frame yet, so here is the QR version

Edit latest Mk3 nomad has swapouts and disc, so thru axle probable if you don't want a rohloff.
Hmm, the one on the tandem looks different, unicrown and no thru axle.
In the description it says:
Available in 3 different offsets to suit the following Thorn frames;
- Mercury Mk3
- Club Tour Mk5
- Nomad Mk3
So I guess the fork isn't from a particular bike. Or the description is wrong.
I can't make any sense of the Thorn website...