STEP is a generic CAD output file from most CAD systems dealing with geometry.
These files maintain the exact intelligence of the structure.
Most applications that can import STEP [.stp] can export STL.

Good you found an answer SS...
I can't for the life of me read the data from the tiny postage stamp image allowed in these forums for newcomers.

...Looking real hard I can kinda see a 9" diameter and 1/8" walls. I'm gonna have to find a way to print flexibles with my printers

Good luck with your project!