the upper inside diameter is .67 in about six different places.....the upper outside diameter is measuring .78 to .785 in several spots around the circumference..... expect along the bottom where the "step" is.... I am getting a solid .79 all the way around it there....with the dial caliper laid flat on the step. But, it doesnt look tapered
I can tell you.... with the glass tube laid vertical on end, on a table.... I can actually get it to rock on its edge.... ever so slightly.... flip it 180 degrees, putting the other end on the table.... it does the same thing....
Clearly the machining was spent on the metal parts. They are obviously relying on the O-rings to fill the gap between the o ring channel - the O-ring - and the inside of the glass tube...
The thicker bottom part... I am geting a .87 pretty much all the way around, outside diameter. Twice out of six I got the dial to fall just a half a hair or so past dead center of the line - making it maybe .872 -.873
Inside diameter - I am getting .70 in three places , and a solid .71 in three places....
My 6" caliper only measures accurately to .99" on the dial, with no finer increment between each .01" hash mark. It's rarely ever used... But mot a machinist dial caliper.
However, The inside measurements are what matter... especially for the bottom of the tank.
The inside of the steel top cap ( drip tip holder ) measures a clean .79" all the way around its inside. So - .785" isn't out of the ball park as far as accuracy goes.