This is a Spinner Adapter Kit by Great Planes.

FEATURES: Adapter kit for aluminum spinners
          This steel adapter kit tightens the backplate & propeller onto the
            engine, then using a single bolt-on design, holds & centers each
            spinner perfectly on its baseplate.
          Machined for accuracy
          Includes aluminum bushing, prop washer and prop nut
          This spinner adapter kit will fit the following engines:
            -O.S. .60FP
            -O.S. .61 FX & .61 SF
            -SuperTigre .61-.90
          One year quality guarantee
          Installation instructions provided on the header card

INCLUDES: (1) Propeller Nut
          (1) Propeller Washer
          (1) Aluminum Backplate Bushing

REQUIRES: 12mm Wrench To Tighten Propeller Nut
          Aluminum Spinner w/Center Mounting Hole
          10-32 Bolt

SPECS:    Shaft Size:       5/16-24
          Prop Nut Length:  15/16"  (24mm)
          Backplate Bushing Inner Diameter: 5/16"
                            Outer Diameter:  3/8"
                                                                    JAL 4/20/99
                                                                          ir/jl
                                                                      kr3/20/03