This roller was built by John Fowler of Leeds in 1915, being delivered to Monmouthshire Rural District Council on 17 November of that year, ownership passing to Monmouthshire County Council on 1 April 1930. At an unknown date it was sold to Bower Brothers, contractors from West Bridgeford, Notts, who in turn sold it to the late G T Dabell of Gotham, Notts during 1960. In 1974 Mr A Reader of Cherwell, Notts purchased the machine and undertook major restoration work.

June 1983 saw the machine purchased by Quainton Railway Society members, and brought to Quainton. It was seen around the centre in steam in summer, and used by the society for work around the site, for many years. It was registered for road use, carrying the registration number AX 3512, and so also occasional visited traction engine rallies locally.

The machine is known as a convertible because the roller itself can be replaced by a pair of road wheels to enable use as a tractor. Unfortunately the wheels were not in the hands of the owners, whilst the engine was at Quainton. AX 3512 weighs 13½ tons in working order, that is with full boiler and carrying two hundredweight of coal and one hundredweight gallons of water. Feed to the boiler is via a crankshaft driven pump or the injector. The engine is a compound, with one small high pressure cylinder and a larger low pressure cylinder. Braking is by means of a handwheel operated hand brake or by reversing the engine.