The mounting industry does not have an official standard but the AMPS pattern might be as close as you can get. The AMPS pattern is a series of four holes aligned in a rectangular pattern. Some manufacturers use two of the four holes while maintaining the AMPS pattern spacing dimensions. Manufacturers that have mounts that align to AMPS are RAM, Arkon and Pro-clip. There are many others as well.
The AMPS pattern consists of four holes located in a rectangular pattern spaced 1.188″ by 1.813 inches. Some manufacturers also have 2-hole adapters that support the diagonal measurement of 1.912 inches. The AMPS pattern is fairly well known in the HAM Radio industry where many head plates use that 4-hole pattern. Another common AMPS compliant area is satellite radio. Almost all of the recently introduced radio cradles have the 4-hole AMPS pattern on the back.
Certain manufacturers like RAM have made almost all of their custom cradles AMPS compliant and use a series of AMPS adapters to attach it to their ball and socket mounts.
The AMPS mounting pattern
AMPS Camera Attachment
The back of a Sirius cradle with Arkon’s AP012 adapter
RAM’s RAM-B-347U AMPS adapter with 1″ Ball
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