Many high end distributors, such as this unit from MSD, feature a moveable collar which helps you dial in the correct engagement between the distributor gear and the drive gear on the camshaft. This is an extreme example, but a good one nevertheless. Notice how worn the brass distributor gear is on this unit. Although it’s way past time that this gear should be swapped out, it still did its job. The brass gear is designed to sacrifice itself instead of wearing the drive gear on the camshaft. This brass gear can be swapped out quickly and without much cost, meanwhile the drive gear on the much more expensive steel camshaft is still in good shape.