This came home with me yesterday:
I found this at an Estate Sale today.
Nice finds, guys!

(And sorry for the late replies. Somehow I missed or never got Alerts for this thread being updated.)
The unbranded chromed 1/2" hex head was included in the sale and I thought it was just tossed in there, but now believe it and the cross bar go together to form a sliding T--which means the Junior's original cross bar is MIA. Those of you with a Junior, could confirm this by checking if your cross bars have a center detent, a ball catch at one end and a pinched stop at the other.
Pinch stop, no groove. I don't see any Billmont literature showing a sliding T, just the short and long T's.
As noted above, the box needed restoration
And it turned out gorgeously!
I'm guessing it is a No. 300 set...
What are the dimensions of the box?
I see that various catalog images show the No. 300 set with a compartment, which is strange, since it came with no handles, but it has the same number (24) and assortment (17 hex; 7 square) of sockets as the No. 100 set, which includes the Master Wrench (MW). I'm postulating that the box for the No. 300 may have been the same exact box for the No. 100 set, just came with no MW, and maybe a different decal under the lid. Which makes sense for them to do. In which case, you wouldn't know if what you have there was originally a No. 100 (and the MW is missing) or a No. 300 (and it didn't come with an MW).
I guess the Billmont merchandising scheme was for a customer who already had a No. 0 (MW only, no sockets) or No. 1 (MW and five (5) sockets), but wanted more sockets, could purchase the No. 300 for the full complement of twenty-four (24).
Individual handles were for sale, and the No. 200 set was all the handles, but only handles, and no sockets, which may be how your incomplete No. 100 or complete No. 300 ended up with a No. 2 Junior Wrench (JW). They did not offer any set with full socketry and the No. 2.
Doing some quick math, a person could acquire all the socketry and all the handles by buying a No. 0, a No. 200, and a No. 300 for less than the $44 smackers the No. 500 set would set them back. But barely (~$5 differential) and no box to put everything in.
The No. 100 box measures 16-1/2" x 6" x 2".
Also, if anyone has an extra Master Wrench they would consider trading/selling, let me know!
I have one, but it's inside this incomplete (missing six (6) hex sox) and trashy No. 100 set box.
At least I think it's a No. 100. It came with the No. 0 MW, which had no sockets inside, but using the same logic as above, that may have been purchased separately by a PO. It had the correct wooden socket tray originally, with all the size markings, but I cannibalized that and a few of the sockets to help complete the No. 500 set.
I also have a spare No. 6 Rim Brace.
I'd probably be willing to let the whole shebang go for a decently agreeable value, but I am loathe to remove just the No. 0 MW, which would neuter the set, and I realize that's probably not desirable on your end, because you don't need the box, and it doesn't even have the hooks if you wanted to cannibalize them!
On top of that, the No. 6 Rim Brace does not fit. Speaking of fit, I'm not sure you can get a No. 0 MW
and a No. 2 JW inside the compartment in that box. So you'd have a complete No. 100 set, and an extra No. 2 and No. 6 handles toward a larger set, that you'd have to store on top.
Interestingly, the backs of the small hinges are marked with Stanley's Sweetheart logo. This adds weight to the dating of the box between 1920-22.
That is interesting. My No. 100 box has different hinges. Or same hinges, perhaps, but no SSH logo.

