Mounted ringcaps on bagpipes are not only pretty to look at. Their real serviceable purpose is to stabilize the other wood they are set on.
When playing, the wood absorbs the moisture from the breath and so it changes minimally. This can lead to tension in the bagpipes. Especially at the tenon connections, where wooden parts are inserted into one another.
The rings are mounted and are holding the material together.
Most of the time, wood for the ringcaps is used that has a contrasting color to the wood that is mainly used, but attention is also paid to the density or hardness, which in principle must be higher than that of the wood to be protected. This means that every now and then materials such as bone, antler or metal rings are used.