Sensenich 82RS72 Hub Varient Question

[roland.t.reimer]

Pictured are two Sensenich 82RS72 props. This design is meant for the Grumman Widgeon.
My question is why one has a flat hub face where the other is routed to form a bezel. Is this for fitting a spinner? The routed hub is also routed on the rear face of the hub.