Well, they actually are
100 amp fuses in a 100 amp disconnect, but...
They're "extremely fast acting" fuses, designed to protect semiconductors (inverters and the like).
They're meant to be bolted into a fuse block,(in which case the writing would show). This goofy guy got fuse reducers, and you can see the results.
Coupled with the fact that the panels are GTE/Sylvania (Zinsco) bolt-in models, the selectivity certainly leaves something to be desired
In the early life of this panel, it was under a pretty high load, with a lot of incandescent lighting and a 10hp fountain pump.
I noticed the arcing and sizzling sound while standing in front of the panel while it only had a 5 or 10 amp load on it.
Randy, I don't think that an allen wrench was ever applied to these lugs. I think that they were possibly just spun down with a screwdriver...S