501 vs 531

not sure but.....Reynolds 531 is a manganese-molybdenum (MnMo) steel, seamless tubeset that has been available since the 1930s in both plain and butted tubesets. The butted tubesets were avaible in several different wall thicknesses. Reynolds 501 was a chromium-molybdendum (CrMo) steel, seamed, butted tubest that made it's debut about 1983 and was available in two different thicknesses. Both tubesets have long been superceded by more advanced steel tubesets, but Reynolds still makes 531 to special order.

Reynolds used to tout manganese-molybdenum as superior to the chromium-molybdenum used by their major competitors, but eventually produced the 501 tubes using chromium-molybdenum. Both are very good steels.

The 531 sets were seamless, which is theoretically stronger, but is expensive to manufacturer, particularly for butted tubing with varying wall thickness. The 501 set was less expensive to produce because the the material was rolled to the varying wall thickness as a flat sheet, which was then fomed into a tube and welded along its length. While purists prefer the seamless tubes, I have yet to see a seamed, 501 tube fail and have no qualms about riding it.

Reynolds 531 was available in several wall thickness, but the baseline 531(c) tubeset had slightly thinner walls than the baseline 501 tubeset. As a result, the 531 tubeset was about 225g lighter.

In general, 501 was aimed at the mid-range market. Hence the slightly thicker and heavier tubes, seamed construction and in Reynolds' opinion, inferior CrMo steel. 531 was aimed at higher models, though it could be found on mid-range models by using plain gauge tubes or combining a 531 butted main triangle with lesser grade stays and/or forks,