I saw this on one of the 3Rensho in the for sale forum (FS. 3Rensho, Full Dura Ace AX, pantographed bits)

Is this type of cable guide available anywhere that people know? Is it specific to the Dura Ace RD on there? I'm not sure it would help keep the cable out of the way when running 9s+ on a frame with a top of chainstay cable stop (I haven't done this but anecdotally seems to be an issue), but it definitely looks neat and tidy!

Specific to the Dura Ace AX derailleur. Maybe 600AX, as well, but DA for sure.

Thanks, that was fast! You're right it's on 600AX too, based on the VeloBase site: VeloBase.com - Component: Shimano RD-6300, 600 AX

Shimano called it a Direct Cable Mechanism and it was used on all four of the AX series rear derailleurs, including Adamas AX and Positron AX to name the other two. The purpose was to eliminate the compression of the cable housing, to increase the speed and accuracy of shifts. It worked really well and I would have liked to see it continued in use but the move was to routing cables under the bottom bracket shell. where an inexpensive, pop-in, plastic guide could replace the much more expensive brazed-on or clamp-on guides used to route cables over the bottom bracket shell. In 1984, Shimano would re-design cable housing to eliminate compression and make it suitable for use with SIS, which moved the indexing mechanism from the derailleur to the shift lever and required constant effective cable length.

Only works for those listed, BTW. Other RD move around and need a flexible housing to allow RD movement. Kinda obvious but sometimes it needs to be said. It is very appealing!

Remember this?