Odd Markings on My 13-3

[Retired W4]

I finally got around to a deep cleaning of my 3" nickel 13-3, with an AEU prefix. There is the assembly number, 26566, which shows up in the usual 3 places, but this mark on the right grip frame is also on the inside right stock panel. It is not the serial number. I realize S&W was not numbering the wood with the gun's SN by this time and this isn't even the serial number.

Has anyone seen something like this before?

 

[snw19_357]

No, I haven't. That's really neat! What are the chances the last four digits of the serial number the revolver those stocks came on would watch the number on the right side of your grip frame.

That number on the right side of the grip is the part number for the frame.

Item #20

 

[Retired W4]

The full SN of the gun is AEU9674.

As an aside, I was wondering when S&W discontinued nickel plated guns. Product Code listings show nickel guns, 3" and 4" into 1986.