As first reported on the 2023 Garage Sale thread, I found this "AJAX" folding triangular index at my flea market this morning.

There are four (4) others on the thread, or at least that show up in a search of "AJAX", owned by
@twertsy,
@d42jeep,
@scooternut, and
@SCscoutguy, and at least one of those displayed photos of every side, inside and out, if you're interested in all the sizes and markings.
One other observation that has not yet been made. That pesky little pin to keep it closed is of course missing on all the examples here except one and that is
@scooternut 's. (They are probably all hanging out with all the missing midget hinge handle cross-bars somewhere!

) I put a brad in mine with just enough of a head to grab and snipped it off short.
Interestingly, and casting the actual manufacturer into question,
@Outlawmws says he has a folding triangular one marked Morse, and
@d42jeep also has the Morse, which he got from
@Shiftless, posted on the Garage Sale thread.
But there is no information on them on this thread, so I did some research.
There was a prominent outfit called Ajax Manufacturing Co, in Cleveland, home of Cleveland Twist Drill and others in the industry. From what I can tell, they made a lot of machinery (forging, boring, etc). But I did see some references to drills that gave me enough ammo to look harder, and their Trademark application in 1906 does include drills.
Having said that, this page from the 1912 Morse Twist Drill catalog is kind of hard to argue with. It's possible Ajax made them for them. The other way around is also possible.
Either way, it's a cool piece and I am happy I found it.