This mount is actually called a " mirror" mount, although it's more commonly used on roof racks and roof bars in 4x4 circles.
They can fit onto either horizontal or vertical bars...
We do two types of this mount, one suitable for round bars, upto 30mm diameter and horizontal only, another for round or square section upto 25mm which can be horizontal or vertical.
Our mounts are heavy duty 4-bolt items which will hold on tight, and not bend or break, unlike those available at some other CB outlets.
In our package deals, this mount comes supplied with a 5m lead, long enough to reach the roofrack at the back of a SWB 4x4 - if you want to fit this on the back of a 110 (for example) you will need our LWB extension lead - see the Related Products links on the package's description.