Bicycle Mechanics - Chainring trivia

Anybody know why Shimano chainrings (don't know about others) have the little rivets, or whatever, out near the perimeter? They look like maybe they're made of different material. They don't attach anything.
:confused:

The rivets, ramps and pins help pick the chain up onto the teeth. They stick out just enough to catch and lift it up.

G

Sometimes there is a pin between the outer chainring and crank, to prevent the chain getting jammed.
The pins are steel, just pressed into a tight hole, and are there to catch the chain and , together with cut-out ramps, ensure fast. easy changing with indexed systems.
My Stronglight chainrings lack these feature, but with an older narrow front mech, and friction changing, they are not so neccessary. Some people call ramped chainrings "pre-worn"

I have regular rings and a few pinned/ramped rings. I also have a Shimano middle 40T ring with two pairs of factory-ground teeth. To those of us who shift only while lightly spinning the cranks, i.e., not under load, ramps and pins make very little difference. Front derailleur indexing is obnoxious.

And that's why some indexing systems will drive you bonkers trying to figure what's wrong with it. Riders tend to innocently ignore checking for ramp wear on the chainrings. Afterall they are alloy.

That makes sense... thanx, y'all.