That is a single size hollow auger. They are used to cut a round tenon. It is much more expensive to have a set of 8 single size ones, but they tend to be sturdier than the adjustable ones. I have seen a lot of broken adjustable ones.
You use the spoke pointer first, so that the end will fit in the hole before cutting the tenon. You can then cut that taper off if you want after you cut the tenon.