Chainwheels on the crank can be riveted (Figure 28) or screwed. When you have to replace cranks with riveted chainrings you should replace both the chainring and the crank.
By cranks with screw chainrings, cranks and chainrings can be replaced separately.
For fixing the crank there is usually a spiderarm.
This spiderarm has four or five arms.
Spiderarms are provided with fixing holes for mounting of the chainrings.
It is even possible with the more expensive models from Shimano to disassemble the entire spiderarm.
At cranks for racing bikes was until recently not common to assemble a third chainring (Figure 31) .
However, there is no little reason to install a third chainring.
Therefore, for racing bikes Cranks get more and more often the possibility to mount a third chainring.
Unfortunately, not all chainrings can be mounted on all cranks.
In order to adjust, the distance of the mounting holes on the cranks and chainrings should be equal.
Nowadays it is possible to provide various types and even the exchange of different brands, noting the number of employed arms on the spiderarm and connection to the crankshaft.
Manufacturers in recent years are quite clear about exchanging components.