Paul McCartney, having grown up with a father who played in a band, was partial to British brass band music. He wrote a brass-band-like film score with George Martin for "The Family Way" in 1966, and two years later composed "Thingumybob" as the theme song for the television series of the same name. The Black Dyke Mills Band recorded the tune on 30 June 1968, and released it as a single on 26 August 1968.
The Beatles themselves never recorded "Thingumybob" in any form.
Interesting, the B-side of "Thingumybob" was the same brass band's recording of "Yellow Submarine".
Confusingly, the order appears to have been swapped by the US releases (pictures of which are above) - meaning that "Thingumybob" was the B-side and "Yellow Sub" the A-side on the US release. The original UK released, however, featured "Thingumybob" as the A-side and "Yellow Sub" as the B-side, as confirmed by Apple's own website:
This blog is a workshop for developing my analyses of The Beatles' music.