So all of my previous bikes had/have fixed, 3-speed or 4-speed. This is my first venture with these new-fangled 5-speeds. When I bought these two, I was just looking at the big cog, I wanted a 24. Now that I am putting them on the on the wheel, I notice the difference between the two.

I assume the one on the right is older. The small cog on the right is flush, on the left, it is an outie. On the back, the big cog on the left is flush, the one on the right is an outie. There are less threads on the right one. When mounted, the one on the left has more clearance from the spokes. I will be using the one on the left for this build.

Can anyone tell me what's going on? I have seen the one on the left in the Regina catalog. What's with the one on the right?