11 mm and 3/8” dovetails are the two most common types of dovetails that you can find on rifles. The 11 mm dovetail represents a standard in Europe, while the 3/8” is a standard in the USA. Some rifle manufacturers have made rifles, like CZ 452 and CZ 453, that have variants with an 11 mm dovetail for European customers and 3/8” for American customers. That is why we are comparing these two dovetail types.
But the difference between these two standards is not only in the measurement unit with which they are named. The “11 mm” in the European dovetail marks the width of the dovetail measured across the top, while the 3/8” in the American dovetail marks the width of the dovetail measured across the bottom as shown in the picture below. The American dovetail actually measures 12.7 mm across the top which means that it is wider than the 11 mm dovetail.
However, that is not the only difference between the two dovetails. They also have different groove angles as shown below. The 11 mm dovetail has a 60-degree angle, while the 3/8” dovetail has a 45-degree angle.
Because these two dovetails have different sizes and angles, regular mounts are not interchangeable between them. But there are some mounts made specifically to fit both dovetails. This is possible due to these mounts having something called a “reversible clamp” which can be rotated to hold onto different dovetail angles and widths.
Very useful information Thankyou