Cartridge fuses for circuits above 60 amps are also known as knife-blade cartridges. They look like rifle cartridges with metal caps and blades sticking out of each end. Cartridges fuses for circuits 60 amps or less are also known as ferrule contact or round cartridge fuses. They look like rifle cartridges with plain, capped ends. Used in high-current applications, such as in the main service box and in clamp- or bar-type fuse boxes that serve electric ranges, water heaters, clothes dryers and air conditioners.