Sierra Lock Nut 5/8"-18, Stainless Steel, Replaces Mercury Marine 11-22339

This Sierra lock nut, part number 18-3713, is a stainless steel fastener sized 5/8"-18 with a Unified National Coarse (UNC) thread, right-hand thread direction, and full thread coverage. It is built with a flange screw head style and a machined finish in black, giving it a corrosion-resistant, durable surface suited to marine environments where saltwater exposure and vibration are common concerns. As a lock nut, its primary function is to stay securely fastened under vibration and load, making it well suited for gearcase and drive component assembly where a fastener backing off could lead to a loose or failed connection. It is used in Mercruiser gearcase and drive applications and is a direct equivalent for Mercury Marine part number 11-22339, allowing it to be installed as a replacement for that OEM part. The stainless steel construction resists rust and corrosion better than standard plated steel hardware, which is important for any fastener used below the waterline or in a wet engine compartment. Each lock nut ships as a single piece for straightforward one-for-one replacement during service or rebuild work.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-3713
• Product Type: Lock Nut
• Thread Size: 5/8 inch - 18
• Thread Type: Unified National Coarse (UNC)
• Thread Class: Coarse
• Thread Coverage: Fully Threaded
• Thread Style: Right Hand
• Fastener Type: Lock
• Screw Head Style: Flange
• Material: Stainless Steel
• Exterior Finish: Machined
• Color: Black
• Weight: 0.04 pounds

Fitment

Used in Mercruiser gearcase and drive applications.

Replaces (OEM)

• Mercury Marine 11-22339

Frequently Asked Questions

What is the thread size on the Sierra 18-3713 lock nut? The Sierra 18-3713 lock nut has a 5/8 inch - 18 thread size with a Unified National Coarse (UNC), right-hand thread.

Does this lock nut cross-reference to a Mercury Marine part number? Yes, Sierra 18-3713 is the equivalent to Mercury Marine part number 11-22339.

What material is the 18-3713 lock nut made from? It is made from stainless steel with a machined finish in black, which resists corrosion in marine environments.

What does this part get used for? The 18-3713 lock nut is used in Mercruiser gearcase and drive component assemblies to keep fasteners secure under vibration and load.

How many lock nuts come in a package? The Sierra 18-3713 lock nut is sold as a single piece, one nut per unit.

Is the 18-3713 a full-thread or partial-thread nut? It is fully threaded along its entire length, with a coarse UNC thread class.

What style of head does this lock nut have? The 18-3713 uses a flange screw head style, which provides a wider bearing surface than a standard hex nut.

Is this a genuine Sierra part or an aftermarket copy? Sierra 18-3713 is a Sierra-branded part manufactured to equal or exceed OEM specifications, offered as a replacement for Mercury Marine 11-22339.

How much does the 18-3713 lock nut weigh? The Sierra 18-3713 lock nut weighs 0.04 pounds.

Can I use this lock nut to replace a worn or damaged OEM nut on my gearcase? Yes, Sierra 18-3713 is designed as a direct replacement for Mercury Marine 11-22339 in gearcase and drive applications.