The 18.1 & 18.7 are bore diameters in mm. Although very faint it appears to me the 1? is also a 14. This would have been the gauge of the bores at original proof. 14 gauge = to .693" 14/1 would have been .701" so the bore would have been between those two dimensions when proofed. Obviously, the 18.1 bore has been enlarged a bit & the 18.7 one a great amount. They were, however, re-proofed as enlarged.

Miller/TN
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