Brian01 - I do not know what brand that you have - but pretty common that 11 mm is the size used on European rifles - so is measured 11 mm across the top of the flat - side angles are usually 60 degrees. North American made, or made-for-export to North America, for some reason, measure dovetails across the bottom - so should be 3/8" across down there, but is very hard place to measure with normal devices. The side angles are almost always 45 degrees. I have rings from Warne - is a "dot" on the clamp - as per instructions, dot is either up or down for 11 mm or for 3/8" dovetails - it fits to either size - I do not know if other makers do that or not.
Go to link below - was discussed previously on CGN - that thread has sketches, etc. and links to other sites with this information:
https://www.canadiangunnutz.com/forum/showthread.php/2041933-Rimfire-dovetail-slotting