The Donuts were invented By Kiwi Squeak Bell who lives in Bakersfield and are stamped out in New Zealand where He still has property and kin. He makes them in mild steel and Stainless. I have used both and they are the Katz Meow! The inside diameter is equal to the pipe diameter (3" tube = 3" I.S. diameter, etc.). They are stamped in two halves and then seam welded around the outside radius.
Kiwi Konnection Hot Rod Parts
(661) 871-KIWI (5494)
925 Bernard St.
Bakersfield, Ca. 93305