This was a design by Seth E. Lover while working at Gibson and used on Silvertone guitars. The pickups were sold OEM (original equipment mfg.) to other companies such as Harmony Guitars. This design was also used on the later pickups designed by Seth when he worked for Fender Guitars. He designed the Guitar and Bass Humbucking pickups and use a CUNIFE magnet. The magnet was machineable and could be threaded and slotted and the pickups were magnetized after assembly.