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:
OS Max 1.08 FSR, FT-240, FT-300 and FR-300, K&B 1.00,
Magnum XL-180AR, Enya VT-240 Twin
INCLUDES: (1) Propeller Adapter Nut
(1) Propeller Washer
REQUIRES: 1/2" Wrench
Spinner Cone & Bolt
SPECS: Crankshaft Thread Size: 3/8-24
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