ah, I missed this in my first search...

"REYNOLDS 525 / 525 OS info

Reynolds 525 non heat treated chrome moly has been in Reynolds inventory of bicycle tubes for many years. Since 1998 it has been reconfigured and up graded to a strength level very similar to that of Reynolds legendary 531 tubing. The primary reason for it existence is its ability to be tig welded, thus producing lower cost and lower quality frames. It has no advantage over 531 except for this singular feature. Jackson does not use this tubing for the 3 main tubes as there is no added benefit to the cyclist.
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I've never looked at this site before. Lots of good, human tubing information here.