45s

LOCATION
Act I, Scene 3, p. 27
REFERENCE
Tracy: "Well, I brought my own 45s, so if you put 'em on, I'll show you my stuff!"

45s are a type of vinyl record. 45 refers to rotations per minute. 45s were typically 7 inches in diameter with a large center hole. They were typically singles, with one song per side. The large hole is for use in a multiplayer machine, where the records would automatically drop down after each song. In the 1950s and in the early 1960s (before the Beatles) teenagers like Tracy collected 45s like crazy. They bought the songs they heard on the radio because of the song, not necessarily the artist. Every record company issued LPs (long-playing records) by their most popular teen artists (e.g. Crystals, Frankie Ford, Bill Haley, Isley Brothers, etc.) in the 1950s and 1960s even if they didn't sell well at the time. 45s were great for a dancer like Tracy who might want to listen to the same song over and over again to get a move right.

SOURCES

http://en.wikipedia.org/wiki/Gramophone_record
http://www.gocontinental.com/pgde.htm