[Kenwood] DFK-3 DFK-3C DFK-7 DFK-7A DFK-7C

[Jerry]

Detachable Front Panel Kits

Does anyone know what the difference is between a DFK-3 and DFK-3C 
and what equipments they can be used on?

Same question for the DFK-7, DFK-7A and DFK-7C?

I have both a DFK-3 and a DFK-7A and am trying to figure out if I can
use them and on what equipments. 

The options section in various equipment manuals  do not show what
the differences are or if they may be interchangeable.

Thanks in advance and take care.  Jerry N6VG