A 3 1/2 inch gauge Heisler 0-4-4-0 to Kozo Hiraoka's excellent design - we've had one or two in before, including a scaled up 5 inch gauge version
(there's some video of it running around at the now defunct Evergreens Miniature Railway in the archive, went like a rocket!).
All have run beautifully, much more capable on the track than their rather quirky looks and American logging railroad ancestory would lead you to believe.
This engine was completed some years ago by, we were told, a dentist - it subsequently passed to a friend who ran it occasionally on air. Unsteamed from new, it runs very well in both directions and is in as-new, unpainted condition.
||3 1/2 inch