MM5.4n Humbucking quad coil 5 string MusicMan®-style bass pickup:

This is a quad coil pickup designed to allow a silent single coil switched operation for either the front or rear coil. It can also run parallel or series, depending on taste.

The industry never really adapted a standard for this style of pickup, and as a result they are available in 3 different spacing and cover combinations

 The 5.4n is Soap-bar shape with no ears and narrow spacing. These have a rectangular cover and narrow spacing that will work on original MusicMan® five string basses.