Shifter Cable Downtube Stop

http://www.wiggle.com/shimano-sti-pair-of-cable-stops/

Save yourself money & don't spend $10-20 on these. They're not worth it.

Designed for 1.125" downtubes. This seems to a very common steel tubing size. My bike is from the 1980s, & it works fine. I imagine you could use a round file to bring it to a better fit if you need.