Bayonet knob in-line fuseholder. Supplied with 8" loop of 14-gauge wire and one spring to accommodate AGC fuses. Simple "twist-lock" allows easy fuse removal and replacement.
Mine was marked Littlefuse Inc P/N FHP1 and came with three springs. Tag says will work with SFE 7 1/2 - 9 - 14 - 20 and 3 AG fuses.
Unit comes with 3 internal springs and only provides codes for which to use. I am using it with a 1A AGC 1 and that option isnt shown. Should call for a fuse LENGTH to determine manufacturer recommended spring. Just makes it more difficult. Otherwise holder is adequate. Sure wish an aircraft part was more insulated from the elements.
This appears to be automotive type wire. No milspec markings.