Its a generic fuse holder that everyone uses and slaps their name on, its not sky highs fault.
These where also not meant to be used with thick lugs, but your typical ring terminals.
If you take the bottom nut off and go washer, ring terminal, nut, washer, fuse, washer, nut it will fit.
It is just a bolt that runs through plastic. It is either molded to the shape of the plastic so it wont spin, or there is a little black circular cap that pops off under each post//bolt and you can than attach a socket so the nut can be tightened back up.
After all, it had to have been done that way one it was built or how else would you get that nut on if it would just spin and spin. Or you can just grind off the ends of the clear plastic piece, which I had to do when using them with 4/0.