Sierra Prop Nut Kit 18-3702, Replaces Mercury 11-69578A1, for Mercury/Mariner Outboard Motors

The Sierra 18-3702 Prop Nut Kit is a replacement hardware kit for Mercury and Mariner outboard motors, designed to secure the propeller onto the propeller shaft. The kit is built from alloy steel with a machined finish and uses a hexagonal, external-hex drive style with a coarse, right-hand M14 metric thread, giving it a commercial grade rating suited to marine propeller hardware. Each component measures 0.39 x 0.39 x 0.39 inches and the complete kit weighs 0.12 pounds.

The kit contains the two pieces needed to reinstall a propeller correctly: a tab washer (Sierra 18-3204) and a prop nut (Sierra 18-3704). These components replace the original Mercury tab washer and prop nut, so boaters can restore the propeller mounting hardware to factory function without sourcing individual dealer parts separately. Because the nut and washer are matched to the correct thread size and profile, the kit helps prevent under- or over-torquing that can occur when mismatched hardware is used.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3702
• Material: Alloy Steel
• Fastener Type: Hex
• Thread Size: M14
• Thread Type: Iso Metric
• Thread Class: Coarse
• Thread Style: Right Hand
• Drive Style: External Hex
• Screw Head Style: Hexagonal
• Grade Rating: Commercial
• Exterior Finish: Machined
• Item Dimensions: 0.39 x 0.39 x 0.39 inches
• Weight: 0.12 pounds
• Number of Pieces: 4
• UPC: 030999256201
• Kit Contents: Tab Washer (Sierra 18-3204), Prop Nut (Sierra 18-3704)

Fitment

Fits Mercury and Mariner outboard motors.

Replaces (OEM)

• Mercury Marine 11-69578A1
• Mercury Marine 11-69578T1
• Mercury Marine 11-69578Q1

Frequently Asked Questions

What does the Sierra 18-3702 Prop Nut Kit include? The kit includes a tab washer (Sierra 18-3204) and a prop nut (Sierra 18-3704), the two pieces needed to secure a propeller onto the shaft of a Mercury or Mariner outboard motor.

Which Mercury part numbers does the 18-3702 kit replace? Sierra 18-3702 replaces Mercury 11-69578A1, 11-69578T1, and 11-69578Q1.

Is the Sierra 18-3702 an OEM part or an aftermarket replacement? It is a Sierra aftermarket replacement kit engineered to replace the original Mercury 11-69578A1, 11-69578T1, and 11-69578Q1 prop nut hardware.

What outboard motors is this prop nut kit for? This kit is made for Mercury and Mariner outboard motors.

What material is the 18-3702 prop nut kit made from? Both the prop nut and tab washer are made from alloy steel with a machined finish.

What thread size does the Sierra 18-3702 prop nut use? The prop nut uses an M14 thread with a coarse, right-hand, ISO metric thread type.

How much does the Sierra 18-3702 Prop Nut Kit weigh? The complete kit weighs 0.12 pounds.

What are the dimensions of the components in kit 18-3702? Each component in the Sierra 18-3702 kit measures 0.39 x 0.39 x 0.39 inches.

How many pieces come in the Sierra 18-3702 kit? The Sierra 18-3702 Prop Nut Kit contains 4 pieces total.

Does the prop nut have a hex drive? Yes, the Sierra 18-3702 prop nut uses a hexagonal head with an external hex drive style.

What is the UPC for the Sierra 18-3702 Prop Nut Kit? The UPC for the Sierra 18-3702 Prop Nut Kit is 030999256201.

Why replace both the tab washer and prop nut together? Because the Sierra 18-3702 kit pairs the tab washer (18-3204) and prop nut (18-3704) together, boaters get matched replacement hardware sized correctly to the original Mercury 11-69578 series parts rather than sourcing each piece separately.