The Railway Series
In 1956, they were borrowed from British Railways to run the North Western Railway while Sir Topham Hatt's engines visited the Mainland. Jinty ran Thomas' Branch Line while Thomas was away and also helped the latter when he crashed into some buffers.
It is possible that Percy knows them from taking trains to the end of the line and telling the other engines stories, like at the beginning of Percy Takes the Plunge.
Stories From Sodor
In Season 13, he came back to Sodor with Flying Scotsman and City of Truro. After an argument in which City of Truro advises Jinty not to be a part of, Jinty decides to get even and attaches a jet engine to the back of City of Truro. He bumped City of Truro and the jet engine hard in order to get the jet engine's lever to go into the "on" position. Jinty was soon punished and had to work around Tidmouth Sheds for the rest of his stay before going back to the heritage railway, the "Great Central Railway."
Jinty is based on an LMS 3F 0-6-0T. Pug is based on an LMS 0F Kitson 0-4-0ST. Their names originate from their classes' nicknames "Jinty" and "Pug". A total of nine 3F 0-6-0 tank engines survive in preservation whereas all 0F Kitsons were scrapped.
Jinty and Pug are painted in the British Railways unlined black livery. Jinty has the BR logo painted on his side tanks.