Close enough, 1/64th is .0156. Yours is a good picture, mine of the 12 ga is not, but the outer rim is touching the extension rib.
The extension ribs for 10-12 ga were all the same width, so if too much was machined off the O.D. for the final fit of the brazed extension rib, there was a problem.

Thanks Bill.

Last edited by JDW; 09/02/10 05:40 PM.
David