Description
Sierra 18-3704 Prop Nut Replaces 11-69578Q1 is a direct aftermarket replacement for Mercury/Mariner outboard propeller nuts, explicitly interchangeable with OEM part numbers 11-69578Q1, 11-69578, 11-69578A1, and 11-69578A2.
Designed for Mercury/Mariner 30 to 60 HP (and up to 70 HP) outboard engines, this part ensures a secure propeller fit to prevent loosening and vibration during marine operations.
Compatibility & Interchanges
The Sierra 18-3704 part is fully interchangeable with several major brand cross-references:
- Mercury Marine / Quicksilver: 11-69578, 11-69578Q1, 11-69578A1, 11-69578A2, 11-69578T1
- GLM: 21240
- Mallory Marine: 9-73901
- Chrysler / Force / US Marine: 11-69578A1
Installation Specifications
- Wrench Size: Typically requires a standard 1 1/16-inch socket or boat propeller wrench.
- Torque Rating: Standard installation on many Mercury outboards recommends tightening the nut to 55 ft-lbs. Always block the propeller with a piece of wood between the blade and anti-ventilation plate before torquing to avoid slipping.
- Hardware Kit Note: The nut itself is often sold individually, but it is also the core component of complete kits (such as Sierra Kit # 18-3702), which bundle this nut with the corresponding tab lock washers (OEM 14-76281 / Sierra 18-3204).
