a magnetic snap latch having a coil wound on a preformed insulating bobbin having anti - rotation projections that locate and fix the coil within a high permeability magnetic shell . a high permeability magnetic plunger extends through a hole in the shell into the coil and has rigidly secured thereto a low permeability magnetic disk within the shell . a high permeability backplate closes the open end of the shell and defines an air gap in which is located a non - magnetic return spring . when the coil is energized , the disk is initially attracted to the shell to move the plunger a small distance to the right but the disk then saturates and the increasing magnetic force in the air gap snaps the plunger to the left , whereafter the return spring restores the plunger when the coil is deenergized .