The AP-01-4.2 Adapter Plate is for use with 274, 285, and 286, and other compatible Arroyo Instruments mounts. The four holes line up with holes on the mount and are intended to be used with M3 x 8mm socket head cap screws, which are included with the adapter plate. Do not use a washer, as it will cause the top of the screw to protrude above the surface of the plate.
The plate is solid copper with hard nickel plating to prevent corrosion and scratching. When mounting the adapter plate to your mount, thermal grease can be used to improve the transfer of heat from the adapter plate to the mount, although it is not required.