Fox Collectors

Hey all,
Quick question on my dad's 12 gauge 1928 Sterlingworth he gave me, serial # 116xxx. Since all the recent topics on chamber length and barrel stampings, I have a question or two on his/my model.
Under the barrel, each chamber is stamped with 3. And there is a concave square next to the serial number. Does this mean the chambers are for 3 inch shells? And what is the other stamping? It's nothing fancy as far as grades go and the top of the barrel is stamped "Sterlingworth Fluid compressed steel" and "Made By A.H. Fox Gun Co. Phila.Pa, U.S.A.
Pictures attached and thank you all!

The 3 on each barrel is the barrel weight of that set of barrels. 12 gauge Fox barrels went from size 0 (most heavy) to size 4 (lightest barrels). 0 weight barrels were only (as far as I know) only on HE graded guns. Most 12 gauge's I've seen have size 2 through size 4 weight barrels with I believe the most common being size 3 (like yours). No idea about the other stamping, but I've seen it on a number of Fox barrel flats.

I would say the 3 is for a 3 weight barrel.

Thank you all! I thought it was chamber length. I'll guess I'll have to have it measured.
It is a joy to shoot with 2 3/4" hand loaded #4 buck shot at cowboy load levels my indoor range allows. Though, my dad rabbit hunted with it using Remington 3 1/4-1-8 loads from the box of shells he gave me. Still tight as a drum and lever is nicely positioned to the right at a good amount of degrees.