Cairns 5A Leather Helmets (Pre-Crash Cap)

[vbcapt]

On the underside of the leather dome is the Cairns metal disk or foil disk. Some of the disks have a small letter on the left side. I was told that this letter indicates the time period when the helmet was produced, anyone know for sure ? If that's the case would anyone here know the times periods for each letter on the disks ?

 

[stretch]

http://www.firehouse.com/forums/t122643/

Scroll down to the next the last post.

 

[vbcapt]

Thanks stretch !