Diazed fuses often have a flat strip of silver/copper in them with holes at certain locations to create a weak point set for the current the fuse supposed to operate at. The screw in bottle type fuse is often filled with fine quartz sand to ensure quenching of the arc. Those fuses can get very hot when running at full load and good clean and tight connections are a must.
The DIN wedge type fuses are also build in a similar way and show the breaking capacity in kA's. Good HRC fuses are 80 or 120 kA rated.
