Thanks for the help everyone. You are most definitely right, because the tab is on a commuter type of bike (Koga Miyata Road Gentleman). So I can imagine some might want a chain guard on that type of bike. There is no chain hanger on that bike. I guess it is because it has a sachs 3 x 7 hub and there will likely never be a quick change. I've been calling these things bafflers because they baffled me. So nice to know what they are for. I'm just learning and really appreciate this site and everyone (well, almost everyone) on here.