As I understand it these were not actual measurements but simply denoted the largest size plug gage which would enter the bore to the required distance. Thus the 108/49 indicates it would accept that size (.350") but not the 99/7 (.360") gage. As noted in the above link some 9.3mm guns of this era will be found with the 118/35 (.340") mark but most likely these were just a little small to accept the more common 118/49 gage.
I have a pre 1912 junker drilling in 8x58 Sauer which carries a 172,28 mark. It would appear thar / , or . are all used interchangably for these fractions.
