R1 was the model name for track-racer and R2 for road-racer.
Those of frames had three kinds of character, Unno D2*D2 tube, Eutectic weld, Double (steel plate) shoulder fork (and round shaped fork).
From 1977, Katakura began to use lugs and Ishiwata 022 tubes for R1 and R2 frame.
Foreigner tends to think that typical Silk must be lug-frame.
It might not be wrong since Katakura had made original lugs by themselves.
However, the lug-less frame which was composed by Eutectic weld and had a Double shoulder fork was the traditional trait of Silk racing bicycle to Japanese Silk fun.
Nowadays, it is too hard to find this traditional Silk Road-racer.
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