twelve-incher
/ˌtwɛlvˈɪn(t)ʃə/(also 12-incher)
noun
Something that measures twelve inches in length, diameter, height, etc.; specifically (a) a cannon with a bore of twelve inches; (b) a twelve-inch record.
Origin
Early 20th century; earliest use found in ‘O. Henry’ (1862–1910), short-story writer (real name William Porter). From twelve + incher, after twelve-inch. Sometimes written with numerical symbol for the first element.