You have a Fidelipac/NAB
Fidelipac, also known as NAB Cartridge, was launched in 1959 and was in use until the end of 1990. We mainly saw these cassettes at radio stations to play commercials, jingles and music.
NAB cassettes came in three different sizes:
Even though the dimensions differed, the mechanism looked the same on the inside. The tape is in an endless loop. With the help of a cue tone, the sound clip can be stopped or initiated.