Thanks, Sawgarage, you are probably right about using the calipers more than I would expect. Growing up building forts by eye with an axe, I am still amazed at the power of measuring tools! Just for the sake of clarity, once I determine the bore diameter, is that the measurement of the ring as well? (i.e. 45mm diameter bore = 45mm ring?)
To Svk, There are no blue or black ink stamps on the top. Pretty sure I checked, but I'll check again. At the base of the cylinder though, cast into the aluminum, is "mahle44n15" and some other digits and numerals I cannot recall in other areas. Don't know if that helps.