The AD-3 is an adapter plate that has a standard 4-hole AMPS pattern on one end that will attach to many VSM Mounts from companies like Brodit, Pro.fit and Panavise. This mount can also be screwed or bolted onto any flat surface like a dashboard.  The other end has a  5mm stud on the other that will thread directly into your Yaesu FT-891, FTM-100, FTM-350 or FTM-400. This is the final piece for a nice clean instillation.