thanks for the info Nevada. That's weird cos it's definitely not that big.
You would think that changing the casting for the seat tube lug would be expensive and difficult, so I expected seatpost size to be the same for most/all Technium MTBs.
I've bought a 26.6 -> 25.4 shim to suit a post I already have.
Weirdly, the frame had a home-made bodge shim already in there - seems like I'm not the only one confused by this bike...