This is a Replacement Locknut Assembly form OS Engines. FEATURES: Durbable steel construction. This helps keep the propellor to stay on the engine in the case of backfire or detonation. The inner nut screws into the outer and locks it in place. The inner nut has threads for spinner mounting. Replacement part suitable for the FT-120 II Gemini II and the FT-160 Gemini-160 engines. INCLUDES: (1) inner prop nut 5/16-24 thread (1) outer prop nut 5/16-24 thread (1) prop washer I.D. 12mm O.D. 35.5mm (1) spacer washer I.D. 12mm O.D. 19mm gab4/5/94