Originally Posted by
kamtsa
What was the difference between IG and non IG chains?
FBinNY's reply about ther revised pin designs needed for chains used with gated and enhanced cogs and chainrings is correct but both HG and IG chains required the special joining pin in 8-speed and newer types.
Shimano recommended the HG chains for road cassettes and IG for MTB cassettes as their sideplate designs were somewhat different. They also said IG chains were satisfactory for use with road cassettes and my own experience bears this out. I used IG90 chains for tens of thousands of miles on various 7 and 8-speed road bikes and they worked very well. They were also available at very attractive prices (often under $15) and were very durable.