This is certainly a great ground connection for the coaxial cable shield currents but the capacitive coupling of a magnetic antenna works pretty well too.
Nmo on roof.
As we move from left to right you will see a nmo mount to be used in a inch diameter hole with a length of coaxial cable attached.
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This install might not have been possible with the normal 3 4in mount but this mount was easier to maneuver into position.
The nmo mount has teeth on the bottom piece which make a good firm connection to the metal of the roof top.
This would be used to mount an antenna on a roof of a vehicle.
Nmo mounts come in various styles and the only difference is how the nmo connector is terminated on the opposite side.