These are very specialised fuses, not your ordinary "glass envelope" type and are often found in high end test equipment such as Fluke Instruments
SIBA - Fuse
Made in Germany
Ceramic body
Part number: 70-172-40
500mA
Type: FF (Very Fast Acting)
1kV rating
Breaking current (rupture current) 30kA @ rated maximum voltage
Used in high end instrumentation, very fast acting and able to handle very high initial surge currents
NEW
Old Stock