Abstract: The present invention relates generally to a three chamber ferrule type fuse comprising a tube of dielectric material having a tube wall and a bore, providing a unitary sub-assembly comprising a plunger and plunger guide, and two short circuit elements, a coil spring and a ring, having the tube wall staked forming a support for the ring inserting the sub-assembly into said bore of the tube so that one end thereof rests on said ring, having the coil spring under compression, and staking the sub-assembly in place. The construction facilitates assembly by automatic machinery.