Originally Posted by
Steve_sr
I was referring to the square joint where the ring meets the crank arm. I don't believe that generic rings have that.
I can only think that you are referring to the "ledge/shoulder" that the rings fit around, quite standard; That is both for a visually "smooth" outer and inner surface once assembled, and to center the rings rather than only rely on the bolts (auto analogy: "hub piloted" versus "lug piloted"). My 50/34 double, available with steel or aluminum chainrings, I have steel (thinner rings inboard of the teeth), the ledges are designed to accommodate the thicker aluminum rings, so a bit of ledge sticks out beyond the rings on both sides. Works fine.
You've got a lot of room in the inner chainring bolt circle, to go a lot smaller. Like you have, closer gap between inner and middle, than middle and outer, just gives you more duplicate gears (though may be proper for same percent difference). The wider the gap the better, IMO (to reduce duplicate gears), provided the system will accommodate that. By the way, what you currently have is the opposite of "half-step plus granny".
Seeing pictures posted of that crank, that may be the last great Shimano crank, one that I would buy. I don't like the assym 4-bolt cranks, both aesthetics, and construction.