Never heard of "the hubs of Hell", but here's what I could find:
"Hotter than the hubs of Hades
Posted by RRC on June 16, 2008 at 15:59
In Reply to: Hotter than the hubs of Hades posted by Victoria S Dennis on June 16, 2008 at 12:58:
: : : I don't find "hotter than the hubs of Hades" in Phrase Finder. There's some speculation on other sites, but this is the one I trust. Does anyone have a definitive answer? It seems to be fairly common in the U.S (I first heard it over 50 years ago).
: : The word "hub" in this expression is a variant of hob, which means principally, according to the Oxford English Dictionary, "In a fire-place, the part of the casing having a surface level with the top of the grate." It is where you put things to keep them warm without burning up. I think, however, that being put on the hobs of Hades does put you in danger of burning up or at least of getting much too hot.
: : I don't think the expression is heard much in the U.S. nowadays. You'll more often hear, "hotter than the hinges of Hades."
: : SS
: This is a euphemism for "hotter than the hobs of Hell" which is certainly the earlier version. I've also come across "black as the hobs of Hell" in 19th-century literature. The hob of a fireplace is proverbially a black hot place, as is Hell; logically the hottest and blackest part of Hell should be its hobs. (VSD)
In the southwestern US here, I hear "hubs of hell" a lot and never hinges nor any variation with Hades. There must be regional differences."
And this:
As hard as the hobs of hell
Posted by Baceseras on October 16, 2007
In Reply to: As hard as the hobs of hell posted by Smokey Stover on October 16, 2007
: : I have heard s saying oft quoted in my family (which is based in Ireland):
: : 'As hard as the hobs of hell'
: : Of course it could be likely that this is a perversion of another saying.
: By another saying, are you thinking of "hot as the hinges of Hades"? It would make a little more sense to me if the saying quoted in your family were, "Hot as the hobs of hell." Hobs (or hubs) were surfaces in a fireplace or on a stove where things could be set in order to get warm or stay warm. They were hard, of course, since they were used as supports. But how hard does hard have to be for this purpose?
: SS
I heard "the knobs of hell", not hobs; and what were those knobs --- budding horns, perhaps?
I don't know if they were Irish at the root (not the horns, but the folks who said "knobs of hell"): possibly Scotch-Irish, by way of Appalachian.
And then there's this:
"My mother-in-law used to always use the phrase, “hotter than the Hubs of Hades”. Now, due to vocal exasperation from her daughter and my constant query, “exactly how hot are the Hubs of Hades?” she has quit using it. I really don’t think I will be getting an answer from her, so I turn to you, Jellies. How hot are they?"
"They’re actually kept cooler than the ambient temperature of 666. It might be an engineering snafu, but the hot tubs melt around 583 degrees, well before 666, leaving a hot puddle. Nobody likes a hot puddle. So, to contain the water, they actually cool it to a brisk 550 degrees. People go hot-tubbing to cool down.
It’s a bit of a misnomer really."