Great Planes 2-1/4" Nylon Spinner with Aluminum Backplate, Yellow Sturdy aluminum backplate holds the spinner in round - which means it turns truer, with less vibration. The engine shaft hole is stepped from 5/16" to 1/4", to perfectly center the opening if enlarging is needed. No spinner nut required. Available in 6 diameters, each in 4 different colors.