The Fender humbucker was designed by Seth E. Lover who also designed the popular P.A.F. humbucker for Gibson in the 50s. Seth later worked for Fender and designed the Fender humbucker using a Cunife # 2 magnet rod magnets. It was used because it could be threaded, slotted, plated and used as an adjustable polepiece. The Cunife magnet was developed in Germany in 1937. The properties of Cunife 1 and Cunife 2 are as follows:

Cunife # 1 60 Cu 20 Ni bal. Fe

Cunife # 2 60 Cu 20 Ni 2.5 Co bal. Fe