Many Spinners come with a little plastic selection of inserts designed to slip into spinner back plates and allow for many different propshaft size diameters.

These can in some cases to serve in the exact same way for propellors.

Landing Products propellors (APC) in the case of the C-2 and the D-1 hub designs actually come with two stepped holes within the hub. The larger hole approximately half way through the hub is in fact the referance true hole for centering referance. There are machined aluminium center rings or inserts with the appropriate size crank hole that fits the larger centering hole. The small diameter portion is drilled out and the ring will now index the prop correctly to the prop shaft even if you use a toilet auger to drill

Most do not bother with this but that is what the stepped hole in your APC's is all about.

John