Instead of using a multi-piece mold insert on their dome mounts, FireStik designed their mounts with a one piece insert. 

The chances of developing internal resistance is totally eliminated as is the possibility of having water leak through the center to corrode connections or ruin the inside of your vehicle. 

They also molded this piece using glass reinforced nylon for durability, strength and longevity.

The mount fits a standard 1/2" (13mm) hole so you can use it on all common mounts (mirror mounts, flat mounts, stake hole mounts, etc.) or by itself as a stand alone mount. 

It includes a rubber seal as well as an underside support washer. 

This mount has a 2" (51mm) diameter base, and when installed with the rubber seal in place, stands a little over 2" (52mm) tall. 

The DM-4A requires that the coax cable be terminated with a PL-259 connector on the mount end as well as on the radio end. 

While this adds convenience to the installation, it also requires more space on the underside, about 0.95" (24mm) not including the space added by the connector.