Originally Posted by
Kontact
126 spacing was for standard 6 and ultra 7 freewheels and cassettes on road bikes. All of the 7 speed stuff was about 5.0 spacing - Shimano and Suntour.
About.
7 speed is all narrow or "ultra" spaced, that's why it will fit in basically the same space as a standard 6. But there are a few differences between 7s.
The overall widths are about the same. Shimano/Sachs has the same spacing all the way across. Suntour's outer two spacers are thicker than the inner four though. This makes it tough to dial in the shifting across systems.