Handy,thanks for uploading

The crank shafts have a radius on the shafts that come out of them to prevent the shaft from breaking under stress. Machined parts should have a nice radius and bolt holes should have a small countersink to prevent cracking. You can see that the inner sprocket has a countersink on the inside to fit over the radius. High grade bolts put a small radius where the threads end and under the head to make them resistant to breaking.