This Is An X-Long Propeller Adapter Nut from Dave Brown Products.

FEATURES: Plain black, CNC machined steel construction.
          Use with 3-1/4" to 4" spinners.
          This prop adapter kit tightens the backplate and propeller onto the
            engine, then using a single bolt-on design, holds and centers
            each spinner perfectly on its baseplate.
          Will fit the following engines:
            All YS 2-Strokes, OPS Maxi .30, Webra .61-1.20

INCLUDES: (1) Propeller Adapter Nut
          (1) Propeller Washer

REQUIRES: 1/2" Wrench
          Spinner Cone & Bolt
          Backplate
          Propeller

SPECS:    Crankshaft Thread Size: M8x1.25
          Nut Length:             1.625"

COMMENTS: Although it will depend on the thickness of your prop and the
            spinner size, as a general rule, always use the longest adapter
            nut possible.
                                                                    JAL 4/28/99
                                                                          ir/jl
                                                                      kr2/26/03