12 in. is the RIAA standard for 33⅓ rpm records. The spindle hole is 0.286 in. (7.26 mm). 33⅓ rpm was first used for movie soundtrack discs, then later for long playing (LP) microgroove records like this one. LPs were introduced by Columbia in 1948.

Vinyl was used in early RCA transcription discs, but only became standard with the introduction of 33⅓ LPs and 45 rpm singles.