Pan/Shovel swingarm frame tubing size?

[oneuptom]

When was the switch made from imperial size tubing to metric size tubing?

I was thinking of piecing a frame together using a 48 Pan front, 81 Shovel middle & a 61 Pan drop-seat rear when I noticed the 81 Shovel frame tubing was metric, no longer imperial sized.

[JBinNC]

Hint:

It ain't metric.

Jim

[oneuptom]

That was helpful!..

[JBinNC]

I live to serve.

Jim