I have both senn HD600s and ety4s earpieces...they attach the cords similarly, with pins of different diameter and with annular grooves near the tips, and both are of different diameter...Hmmm,let me get my micrometer out...
On the Senns, thick pin is .0625 inches, small pin is .0500 inches in diameter...
On the ETYs, the thick pin is .0502 inches, and the small one is .0401 inches.
However, both sets of pins are remarkably similar..they both extend out the exact same distance out from the plug, and they are both grooved in the same relative position. Both sets are gold plated...
I'll bet that both companies use the same supplier for the pins, and I would put money on it being a medical instrumentation company...
Will keep looking...
My brother is a custom jeweller...maybe he could cast/form/machine some out of gold/silver for us...
Will get back to you.
Edited measurements...smoke in the cockpit for previous measurements?.