David Goerndt wrote:
> I found a similar marking on my '67 PX 10, with the addition
> of the numbers 19/22.
This is the wall thickness in wire gauge; it corresponds to 1.0mm butt, 0.7mm unbutt. Lightweight handcrafted frames often used 20/23 (.9/.6) for the downtube, and 21/24 (.8/.55) for the TT and ST. Note that wire numbers get bigger as the wall gets thinner.
I think it was sometime in the 80s the Reynolds and Columbus both stopped stamping the numbers and went to an electrical process that writes the numbers in what looks like ink. The stamping is often readable through the paint, but the new style isn't This new style is always lost when sandblasting, and can be taken off with an acid pickle if the builder used one, so it's rare to see them on a stripped frame.