Axis has introduced a carbon mast to its mast lineup in 2020. This means that they had to redesign the fuselage and consequently this "doodad" is required if you have the original 19mm alloy mast or the new slim 16mm alloy mast.
The "doodad" is essentially a removable spigot, replacing the earlier version. The "doodad" is not required at all if you choose to run only carbon masts.
Machined to provide equal stiffness as the original, but with substantial weight savings.