Unlike most screw caps, the three point screw top had three lugs jutting out from the lip which were to engage a metal cap.
This closure can be found on Whisky and medicine bottles of the 1837-1940 period.
One approach to helping beginner identify their old bottles involves show them the bases of old bottles.
The picture below at the left shows an iron pontil on the base jof a historical flask circa 1865.
I have put up pictures of the lips so that the readers can see how they mold goes all the way over the top as shown below. This is different than an older hand tooled, hand blown bottle.
The pressure from the automatic machine was strong and the molds fit tight leaving only a very thin line.
In the 1920s, the bottle mimicked early forms which were hand tooled and sealed with a cork.Both the front and back has a small white 7up sheild on the neck. It was their Duraglas product which was used for beer and other bottles that were refilled many times.It stands 8" tall, is 2-1/4" across the bottom and it held 7 fluid ounces.The disk-like mark is sometimes confused with a pontil.the pontil is actually broken glass where the metal rod used to hold the bottle while the lip was form was broken off leaving a sharp scar. The glass is green in color and uses an applied color label (ACL) on both sides.