Replacement top gearbox nut fits 436 different Bush Hog models, used on both input and output shafts. Please see fitment list below. If you are not sure this is the correct nut for your application please contact us and we will help you make sure it is correct. The part fits the 436 models listed below: 109 Rotary Cutter - 79 Left Side Gearbox (540 RPM) Used On 109-OR, 109-OS, 1209R, 1209S 109 Rotary Cutter - Gearbox Assembly (Center) 1000 RPM 109 Rotary Cutter - Gearbox Assembly (Center) 540 RPM 109 Rotary Cutter - L.H. Gearbox Assembly (540 RPM) 109 Rotary Cutter - Left Side Gearbox Assemblies (540 RPM) 109 Rotary Cutter - Left Side Gearbox Assembly (1000 RPM) 109 Rotary Cutter - Right Side Gearbox Assemblies (540 RPM) 109 Rotary Cutter - Right Side Gearbox Assembly (1000 RPM) 109 Rotary Cutter - Gearbox Assemblies, Left Side (540 RPM) 109 Rotary Cutter - Gearbox Assemblies, Right Side (540 RPM) 109 Rotary Cutter - Gearbox Assembly (Center) 1000 RPM 109 Rotary Cutter - Gearbox Assembly (Center) 540 RPM 109 Rotary Cutter - Gearbox Assembly, L.H. (540 RPM) 109 Rotary Cutter - Gearbox Assembly, Left Side (1000 RPM) 109 Rotary Cutter - Gearbox Assembly, Right Side (1000 RPM) 109 Rotary Cutter - Gearbox, 79 Left Side (540 RPM) Used On 109-OR, 109-OS, 1209R, 1209S 109-Offset Rotary Cutter - 79 Left Side Gearbox (540 RPM) Used On 109-OR, 109-OS, 1209R, 1209S 109-Offset Rotary Cutter - Gearbox Assembly (Center) 1000 RPM 109-Offset Rotary Cutter - Gearbox Assembly (Center) 540 RPM 109-Offset Rotary Cutter - L.H. Gearbox Assembly (540 RPM) 109-Offset Rotary Cutter - Left Side Gearbox Assemblies (540 RPM) 109-Offset Rotary Cutter - Left Side Gearbox Assembly (1000 RPM) 109-Offset Rotary Cutter - Right Side Gearbox Assemblies (540 RPM) 109-Offset Rotary Cutter - Right Side Gearbox Assembly (1000 RPM) 109-Offset Rotary Cutter - Gearbox Assemblies, Left Side (540 RPM) 109-Offset Rotary Cutter - Gearbox Assemblies, Right Side (540 RPM) 109-Offset Ro