Hi David,
I have a Reynolds Tube catalogue, there's no date but it has a TI (in a
circle) bug. Judging from the catalogue layout, 531 is the top tubing. 'A'
and 'B' follow. 'A' has butted and 'A' and 'B' have plain gauge frame tubes.
'A' continues with "Quality Seat and Chain Stays" as well as 'A' Quality
Taper Gauge Fork Blades. 'B' Quality Plain Gauge Cycle Front Fork Blades are
listed also. It must be a price point issue. 531 being the best, 'A' and 'B'
following as lower price point products.
Stevan Thomas
Alameda, CA