The pilot of the stump planer auger bit takes the most punishment as it engages with the stump and help draws the planer down into the stump. Since it comes to a point, it can get worn down over time. It can also snap the end off if there is too much movement while in the stump.
The pilot tip only can be replaced – or the whole assembly including the two cutting edges can be replaced. See the parts breakdown for more information.