I stumbled across this Sauer/Krupp 3 Ring Steel certificate on Gunbroker, http://www.gunbroker.com/Auction/ViewItem.aspx?Item=243575253 , and it goes a long way to define that Sauer used a data string(123.28 - #123 or 1928) on the lower rib(and I think I've seen it on the individual tubes) for their Krupp Aktiengesellschaft tubesets:





Interesting Belgian proof certificate also.

Kind Regards,

Raimey
rse