I am familiar (we are all familiar) with the standard figure-8 shape of a chain link.
I also somewhat understand the justification for the "flat-top" chain link.
This style is used when the link is too narrow, and the flat-top adds material that makes the chain sturdier. This material will never be in contact with the chainring or the sprockets. If anyone ever thought of extending the life of a chain by using the other side (a futile endeavor), this style will at least dissuade them.
In the preceding two styles, importantly, all chain links look like this, whether they are the regular links or the pair used to join the chain ("power link" in SRAM's jargon).
But there is also a style we could call "convex top".
What's the story of this style? In particular:
- Only the power-link looks like this. The remainder of the chain is a figure-8 style. Hence it can't be for additional strength; can it?
- It looks like it would wrap around the chainrings and, especially, around the sprockets more tightly. Is the idea to make the chain pull act in the direction of the slant in this style of power-link's offset-from-the-main-line notches?
- Is it necessary to use that style with all 12s SRAM? Can another style be used?
- Chain compatibility is usually good. Any 11s chain can be used with any 11s system. Is the use of this style optional or mandatory, and can it be used with Shimano, or can Shimano's (or KMC's, ...) 12s chains be used instead, along with their own connectors, in a SRAM 12s system?