Historically used in the construction of masts and booms for wooden boats, the bird's-mouth joint is straightforward to make, stronger than a traditional miter and, with nesting joints, easier to glue up without shifting.
With these three cutters, it is a simple matter to make 6, 8, 12 or 16 sided hollow columns, as well as straight or tapered multi-sided planters, bowls, etc., all of which can be left multi-faceted or planed / sanded round. Generally, more sections are required for larger-diameter assemblies to keep the wall thickness to a minimum, and reduce the amount of material to be removed when rounding.
Designed to produce flush joints with material up to 7/8" thick. Thicker material can be used, but will require some dressing after glue-up. Holder included with each bit.
For better safety, these bits should be used only in a router table equipped with a fence and not used free hand.