I think that there is no chance a serial # with 1 letter and 3 numbers after it will be a Bob Jackson. They made thousands of frames over many years and would need a much more complex and longer system. Many here must have a Bob Jackson they can tell us what serial number system is on their frame. Sometimes the serial number system is not how many were made from their beginning but rather when it is made. And this can be done in code. Either a letter or number will represent the month and again for the year it was made.

When I visited bob Jackson's shop in 1975 while I was apprenticing at nearby Ells Briggs, George Foster was the foreman builder and he had like 4 (+ -) young builders under his direction turning out a solid number of frames every week. Someone would do all of us a favor by identifying the serial number system builders used. That way if you see a frame with 6 numerals, it is easy to discard brands with a different numbering system.

Kevin Sayles, now a Classic Rendezvous member, worked for Bob Jackson back in the 70's and then became a builder at Woodrups and is now building under his own name. He would have an idea if your mystery frame was made by someone up north.