For tesla coils up to 500kV, 12" diameter x 3" height spun aluminum with ¼" center hole.
These are spun aluminum of grade 1100-O (99% pure aluminum), with a narrow seam around the diameter. The seam is overlapped metal-to-metal contact around the full diameter, which does not effect the arc's emission location. Aluminum wall thickness is approximately 1/16" (so the flat central area is about 1/8" thick, for example). Excellent for Tesla coils requiring a capacitive terminal, and for high voltage DC generators.
Our laboratory has the tooling and now offers many sizes of toroidal terminals: have a look at our PDF sheet to see other available sizes from 3 to 98 inches!
Quantity discounts available -- contact us for more information.