The 0.736 & 0.737 are the bore diameters in inches at time of last proof.
11 gauge = 0.710" & 10 gauge is 0.775". I do not recall offhand if there were one or two steps between 11 &10. Dependant upon that these bore sizes at the time of original proof would have been marked as either 13 or 13/1.


Miller/TN
I Didn't Say Everything I Said, Yogi Berra