I made another version of the same ball tube as above. This is actually the third version.
When I was nearly done with the first version, I didn't know how to close the bottom of the tube. So I just stitched across the bottom. It looked terrible.
The second version above has a circular wood plug in the bottom. But it is just a straight tube, and I didn't like it. It didn't look quite correct. It looks like a damn cigar.
This is the third version. The circumference on the bottom of the tube is a 1/4-inch wider than the top, so it has the same subtle taper as the historical version. When I make another one, I'll expand the difference to 5/16 or 3/8-inches. The turned Maple stopper has a coned transition between the stem and the top, so it gives the top of the ball tube a nice flare. The stopper rests in a deep conical hole in the throat. All in all, I am very pleased with this one. It took only about an hour-and-a-half to make.
I made it from 5-6 oz. veg tan. After dyeing and sewing, I soaked the ball tube in water and then carefully hardened the leather with a heat gun. I left the stopper in place so that the leather shrunk around the stopper. But then I couldn't remove the stopper. You might be able to see my teeth marks on the stopper, I finally got it out. The leather will stretch with time.
I discovered that the top of the stopper, where you grip it with you fingers, has to have vertical, parallel sides. Otherwise you can't grab it with your teeth. If you try to bite a stopper with sloped faces, your teeth just rake off the wood.