Not sure I've seen an Ajax looking quite like this before, it's a "narrow gauge-ised" version of the popular 0-4-0 tank engine which makes it into something "Sweet Pea" sized. It's seen plenty of running, however it steams very freely, still goes like the clappers and will run almost silently one notch from the middle on the reverser.
Silver-soldered copper boiler, working pressure 80psi, feed by axle pump and handpump on footplate. Twin safety valves. Gunmetal cylinders with slide valves actuated by Walschaert's valve gear, sight feed lubricator, rod-operated draincocks. There is a quiet though mellifluous whistle.
There is a clip of it running in the workshop.
Length 35 inches
Width 12 1/2 inches
Height 23 inches