This is a Two-piece Two-Blade Black Nylon Spinner with an Aluminum Backplate.
No spinner nut required. Engine shaft hole is stepped to prefectly center the opening if englarging is needed. Sturdy Aluminum backplate holds the spinner in round-which means it turns truer, with less vibration.
Spinner Diameter : 2-1/4 in.
Spinner Backplate Thickness : 1/8 in.
Crankshaft hole : stepped from 5/16 in. to 1/4 in.