I just went through this with a CZ Scout rifle. From CZ-USA website, CZ used both 11mm and 3/8" dovetails at different times on different CZ 452 receivers. OP has it correct - measure the width at the widest part of the dovetail. Will be 11mm for "11mm dovetails", with be about .500" (say, 12.7 something mm) for a 3/8" dovetail. Warne makes a QD ring that allows you to flip the clamp for either dimension. But if you measured 16mm, you have neither a 3/8" nor an 11mm dovetail.