The 1993 R500 was a 3.0 series frame. I can't say for certain but I suspect the R500 took a standard ISO 1" headset with a 30.2 mm ID. The headset listed for the R500 was the Tange ME-SII, which was also used on the upper end hybrids, the T700, and a number of 1992 models. Fairly sure all...