AMC keys, brands ; what's with the RA-4 and RA-5 ignition keys?

[Gremlingts@xxxx]

 I scored some aftermarket AMC keys in a back-country hardware store, and 
after getting home, I sorted thru them. I have gold ignition keys with RA-4 
on them, and silver with RA-4, both square heads. But, one of the silver keys 
says RA-5, and has different width cuts and spacing of the slotting on the 
key. Both types of silver keys are made by Curtis, and have square heads.
The round key for the trunk/glove box is an RA-3, has the same cut/width 
slot guide pattern as the gold and silver RA-4's, but with a small cut-out 
back by the key-stop where the key widens out some, at the bottom. Maybe a 
way to find the key in the dark? lol 
Any idea what the RA-5 is for? Any key experts on the list? Here's some 
other key brands I have for AMC :

ILCO - no code, square head, igntion/door '74 Gremlin
AXXESS + - key # 16, modern equivalent ignition/door.
Briggs and Stratton hex head - code # 1644 , ignition
Briggs and Stratton round head - code # 1667, rear hatch ( both B & S 
keys look like RA-4 slotting, they fit my '72 Gremlin )
RA-1 - round head, looks like an ILco brand, faded out - fits my '74 
Gremlin locking gas cap. 

Well, that's my handy-dandy key report, anyone know anything about 
RA-5's, let me know. Thanks!

Jerry in Virginia