This is a mysterious document. Unlike a full patent, a Design Patent is not something you take out in the vague hope that something will catch on - you take one out specifically to defend your right to use a very particular 'ornamental' design. It's about exactly what something looks like, not about how it may work. So Ryobi Limited would have taken out this Design Patent to cover the appearance of a real existing detailed design of derailleur. However I have no idea what became of it.

• Publisher: US Patent and Trademark Office
• Inventor: Noritoki Ishikawa
• Country: USA
• Date: Priority date January 1983
• Derailleur brands: Ryobi
• Derailleurs: unknown