T-Mar

Tange OS or Tange Ovesize was the proper name for this tubeset. It was available initially in MTB and road versions, and later in Prestige versions. It had a number of new features to save weight, including shorter butts and tapers,tapered butting at the head tube end of the top and down tubes and the bottom bracket end of the seat tube. The post end of the seat tube used external "bulge butting" for reinforcement, though the literature is not clear and this may be only on the the ATB set? I'd appreciate if you'd check your frame for change in the external diameter of the seat tube, staring 2-3" below the top tube. I don't have any info on the gauges but later in the 1990s, after these sets were dropped from the lineup, it's notable that the Prestige OS set came in gauges equivalent to standard diameter #1, #2 and Prestige.