Halter buckle straight solid brass 10 mm (= center bar) (ea)

Measurements are of the center bar. The inside of the buckle can be slightly wider for these buckles are often used with thicker leather.

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.