Sierra Brass Castle Washer 18-3714, Replaces Mercury 12-31211A2, Fits 135-275 HP V6 2-Cycle Outboards

The Sierra 18-3714 is a brass castle washer used on outboard propeller hardware. A castle washer is designed to work with a cotter pin to lock the propeller nut securely in place, preventing the nut from backing off during operation. Built from brass, it resists corrosion in the marine environment better than uncoated steel hardware, making it a reliable choice for maintaining a secure and dependable propeller assembly.

This washer is intended for outboards rated 135-275 HP with V6 2 cycle engines. It directly replaces several Mercury Marine OEM part numbers, so it can be used as a drop-in service or replacement part when rebuilding or servicing the propeller hub assembly. Keeping this hardware in good condition is a simple, low-cost way to avoid a lost or loosening propeller nut.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3714
• Product Type: Brass Castle Washer
• Material: Brass
• Fitment: 135-275 HP (V6 2 cycle)
• Weight: 0.28 pounds
• UPC: 030999755902
• OEM Cross Reference: 12-31211A2, 12-31211, 12-31211A3, 12-31211Q03

Fitment

• 135-275 HP (V6 2 cycle) outboards

Replaces (OEM)

• 12-31211A2
• 12-31211
• 12-31211A3
• 12-31211Q03

Frequently Asked Questions

What is the Sierra 18-3714 castle washer used for? The Sierra 18-3714 is a brass castle washer used on outboard propeller hardware; it seats against the propeller nut and is paired with a cotter pin to keep the nut from loosening during operation.

What outboards does the 18-3714 castle washer fit? This washer is fitted for outboards rated 135-275 HP with V6 2 cycle engines.

What OEM part numbers does the 18-3714 washer replace? It replaces Mercury OEM numbers 12-31211A2, 12-31211, 12-31211A3, and 12-31211Q03.

Is the 18-3714 washer made of brass or steel? It is made of brass, chosen for its corrosion resistance in marine environments compared to uncoated steel hardware.

How much does the Sierra 18-3714 castle washer weigh? The Sierra 18-3714 brass castle washer weighs 0.28 pounds.

Do I need a cotter pin with the 18-3714 castle washer? Yes, a castle washer like the 18-3714 is designed to be used with a cotter pin passed through the slots to lock the propeller nut in place.

Is the Sierra 18-3714 a genuine Sierra part or aftermarket? The 18-3714 is a Sierra-branded replacement part manufactured to replace the listed Mercury OEM castle washers.

What is the UPC for the Sierra 18-3714 castle washer? The UPC for the Sierra 18-3714 brass castle washer is 030999755902.

Can the 18-3714 washer be used on any outboard propeller? The 18-3714 castle washer is intended for 135-275 HP V6 2 cycle outboards and the specific Mercury hub hardware it cross-references; it should be matched to that fitment before ordering.

Does the 18-3714 come as a single washer or multiple? The Sierra 18-3714 brass castle washer is supplied as an individual replacement washer.