"jim rozen" wrote: But if it were a foot in diameter, then the force at
the center of the plate would be about 1600 pounds or so. The height of the
jar does not matter. (clip)
^^^^^^^^^^^^
We're just kidding around, aren't we? So. I will point out that the OP
specified that the bell jar is about 1/2 gallon. So, if it is a foot in
diameter, it will be about 2" tall. Your force calculation gets the correct
number, but the force will not be at the *center* of the base--it will be
uniformly distributed over the entire area.

The only point I was trying to make in my facetious posting was that the
required thickness of the base cannot be specified unless the diameter is
known.

As a practical matter, a 1/2 gallon bell jar is probably about 6" in
diameter, so it will have a force on it of about 400 lb. I would make the
base out of whatever is available in the range of 1/4" to 3/4", just based
on two things: 1.) You don't want it to "oilcan". 2.) You don't want it
to be too heavy to handle easily.