The Stereo-Pak 4-track cartridge was the forerunner to 8-track cartridges. It was based on the Fidelipac cartridge, the industry standard tape cartridge used at the time for radio broadcasting of commercials and jingles, but used 4 tracks to provide 2 stereo programmes.
It was introduced in 1962 by Earl ‘Madman’ Muntz (a merchandiser of used cars and consumer electronics). Players were usually fitted to cars (including those of a number of celebrities) but home players were also available, and these were capable of using the larger cartridges based on B and C size Fidelipac cartridges. The Stereo-Pak system lasted until around 1970, by which time 8-Track was more popular despite being of poorer quality.
Muntz licensed music by many popular artists from most of the major record labels, and released hundreds of titles in many genres. Columbia Records was one of the few major record labels to release music recorded on Stereo-Pak cartridges themselves on a widespread basis.
The tape is arranged in an infinite loop which traverses a central hub and crosses a tape head at 3¾ inches per second, pulled by tension. The tape is dampened by a lubricant on the back, usually graphite. A lever on the player allowed the switching between programmes. Due to the method the tape is moved, it is impossible to rewind, and often risky to fast forward a 4-track tape.