The design of Locomotive 1243 was close to the British 23 class locomotives of the time with a short free steaming boiler and a high ratio of heating surface in relation to tractive effort. This made it ideal for relatively level roads. In keeping with the British 23 class, the locomotive had a raked smokebox and polished brass helmet dome with Salter safety valves. Different features of the New South Wales-designed-built engine is the leading four-wheel Bissel bogie, instead of a two-wheel pony truck which gave 20% more tractive effort.

The locomotive was modified in about 1899 to improve its steaming capacity. A Belpaire (flat top) boiler replaced the original round top boiler, the raked smokebox was made upright, and a standard cast funnel was added. Following this a new extended smokebox was installed in 1967.

The valve gear is internal of Stephenson's configuration and the Westinghouse brake pump is fitted to the left-hand side of the smokebox. Although originally a green livery the locomotive is now finished in black.

Locomotive Specifications:
Builder: Davey and Company, Atlas Engineering Works, Hay Street West, Sydney
Date built: 1882
Type: tender type, standard gauge
Wheel arrangement: 4-4-0
Class: C-79 later Z12
Number in class: 68
Date in Service: 1882-1955
Tractive effort: 13 100 lbs (58 268 N)
Boiler pressure: 140 p.s.i. (965 kPa)
Cylinders (2): outside, 18 in x 24 in (457 mm x 609 mm)
Steam Pressure: 140 lbs (965 kPa)
Valve Gear: Stephenson's
Leading wheels: 36 in diameter (914 mm)
Driving wheels: 5 ft 6 in diameter (1 676 mm)
Heating surface: Firebox: originally 87 sq. ft (8 sq. m) later 94 sq. ft (8.7 sq. m)
Overall length: 27 ft 11 in (8.5 m)
Overall height: 13 ft 6 in (4.1 m)
Overall width: 9 ft (approx.) (2.7 m)
Brakes: Westinghouse
Total weight of locomotive: 41.3 tonnes

Tender Specifications:
Total weight of tender: 22.3 tonnes
coal: 4.5 tons (4 600 kg)
water: 2000 gals (9 000 litres)