My rough translations of the photo captions, clockwise from top left are:

• SR-II
• Maruishi ST-I
• ST-II
• Maruishi SR-I

Sanko manufactured own-brand versions of its derailleurs for the Maruishi bicycle company.

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• Publisher: New Cycling
• Document: New Cycling May 1981 - '81 Derailleur Collection
• Date: May 1981
• Derailleur brands: Sanko, Maruishi
• Derailleurs: Sanko SR-2, Sanko ST-2, Maruichi SR-1 , Maruishi ST-1