Measurements are of the center bar. The inside of the buckle can be slightly wider for these buckles are often used with thicker leather.
|Title||Halter buckle straight solid brass 10 mm (= center bar) (ea)|
We measure the inside of the buckles, O-ring etc. (= the size of the leather belt that can go through it)
The size of O-rings is the inside diameter, and with the D-rings we measure the inside of the straight side.