Copied from another recent IAP thread.
Standard Sierra bushings are 20A---Sierra Vista bushings are 70A. These 50A bushings are only used on pens w/pre-fitted tubes--the circuit board pen, and the "tropical series" pens (white coconut, brown coconut, abalone, and mother of pearl>)
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Shannon
Pomona, CA
*All stressed up, and no place to blow!*
The bushings that came with my Sierra Vista Abalone kit were labeled as 50A on the printed label; but the "50A" was crossed out and "70A" written in by hand.
My 70A bushings measure 0.521" & 0.550". The hardware measures 0.522" & 0.549". From what everybody has posted, I would bet the bushings are the same physical size; but labeled differently as a marketing ploy.
It will be interesting to see what BB and Ernie have to say!!