Mirror has left-hand thread M8 to be mounted in M10 left-hand thread

• thread on vehicle: M10 left
• thread on mirror: M8 left

The adapter is simply screwed into the mount on the vehicle and the mirror can be mounted.

TIP: To check whether a left-hand thread is available, simply screw a standard nut/screw onto the mirror or into the mount.
Standard nuts and screws have a right-hand thread and cannot be screwed into a left-hand thread.

If the screw/nut can be screwed in, it is a right-hand thread.