Article snapshot taken from Wikipedia with creative commons attribution-sharealike license.
Give it a read and then ask your questions in the chat.
We can research this topic together.
The Highland Railway O Class locomotives were built as 2-4-0Ttank engines, but were soon rebuilt as 4-4-0Ts. They were designed by David Jones for Scottish Railway companies and three were built at the company's Lochgorm Works in 1878 and 1879.
Dimensions
They had 4-foot-9-inch (1,448 mm) coupled wheels, 16-by-22-inch (406 by 559 mm) outside cylinders and weight (in original condition) of 36 tons.
The three locomotives were withdrawn and scrapped between 1928 and 1933.
References
Baxter, Bertram (1984). Baxter, David (ed.). British Locomotive Catalogue 1825–1923, Volume 4: Scottish and remaining English Companies in the LMS Group. Ashbourne, Derbyshire: Moorland Publishing Company. p. 195.
Casserley, H. C. & Johnston, Stuart W. (1974) . Locomotives at the Grouping 3: London, Midland and Scottish Railway. Shepperton, Surrey: Ian Allan. p. 153. ISBN0-7110-0554-0.