PIC 1 -- The two guesses on what the HT over A stands for are 1.
Heat
Treated
Annealed. 2.
High
Tensile
Alloy.
PIC 2 -- poorly struck 1 1/2 for the frame size.
PIC 3 -- Correct.
PIC 4 -- Parker Bros. never added the E on the watertable stamping of the Quality. The 2 under the serial number is the Grade. Grade 2 hammerless guns were Quality GH in 12-gauge and smaller and Quality EH in 10-gauge.
Quality G.H. Blue Ink Catalog.jpeg
Quality E.H. Blue Ink Catalog.jpeg