[simpits-tech] Standard mounting dimensions for avionics?

[Freeman P. Pascal IV]

Is there a standard width for avionics equipment?  I have seen 
everything from 6.25 to 6.35 inches in online product descriptions.  
Simkits uses 6.3 inches.

I've tried to find pictures or installation instructions online for your 
typical King/Bendix units.  How are avionics units secured?  What kind 
of mounting hardware is typical with avionics equipment?

-Freeman