Sierra 18-8404-1 Starter Bolt, 3/8-16 x 1-11/16 Inch, Replaces Mercruiser 10-8053434

The Sierra 18-8404-1 is a marine-grade starter bolt sized 3/8 inch-16 UNC and 1 11/16 inches (42.9 mm) in length, built to secure a stern drive starter to the engine block. It is machined from low carbon steel with a Grade 2 hardness rating, fully threaded along its entire length with a right-hand UNC thread and a Class 1A thread fit, and finished with a hex head for standard wrench or socket installation. This bolt is designed to be interchangeable with Mercruiser Stern Drive hardware numbered 10-8053434, making it a straightforward replacement when the original starter mounting bolt is corroded, stripped, or missing. Its 0.38 inch outside diameter and 3/8-16 thread size match common stern drive starter mounting points, and the fully threaded shank provides consistent clamping force across the full bolt length. Sold as a single bolt, it is intended for buyers who need to replace one or more starter mounting bolts individually rather than purchasing a complete hardware kit. The low carbon steel construction and machined finish are built to hold up to the vibration, heat, and moisture exposure typical of a marine engine compartment.

Specifications

• Brand: Sierra
• Manufacturer Part Number: 18-8404-1
• Product Type: Starter Bolt
• Length: 1 11/16 inches (42.9 mm)
• Thread Size: 3/8 inch -16
• Thread Type: UNC
• Thread Class: 1A
• Thread Style: Right Hand
• Thread Coverage: Fully Threaded
• Head Style: Hex
• Material: Low Carbon Steel
• Finish: Machined
• Grade: Grade 2
• Diameter: 0.38 inches
• Fastener Type: Hexagon Bolt
• Weight: 0.1 pounds
• UPC: 808282202125

Fitment

This is a universal-fit starter bolt sized to fit standard 3/8-16 starter mounting points; it is not restricted to a single engine or drive model.

Replaces (OEM)

Designed to be interchangeable with Mercruiser Stern Drive 10-8053434.

Frequently Asked Questions

What size is the Sierra 18-8404-1 starter bolt? It is a 3/8 inch-16 UNC bolt measuring 1 11/16 inches (42.9 mm) long, with a 0.38 inch outside diameter, making the Sierra 18-8404-1 sized for standard stern drive starter mounting points.

Is the 18-8404-1 fully threaded? Yes, the Sierra 18-8404-1 starter bolt is fully threaded along its entire 1 11/16 inch length, so the full shank engages the mounting threads for consistent clamping force.

What material is this starter bolt made from? The Sierra 18-8404-1 is machined from low carbon steel with a Grade 2 hardness rating and a machined finish.

Will this bolt fit any stern drive engine? The Sierra 18-8404-1 is a universal-fit bolt sized to 3/8-16, so it is not limited to one specific engine or drive model as long as the mounting hole matches that thread size and length.

Is the 18-8404-1 the same as Mercruiser part 10-8053434? The Sierra 18-8404-1 is designed to be interchangeable with Mercruiser Stern Drive hardware number 10-8053434, so it can be used as a direct replacement for that bolt.

Does this come with a nut or washer? No, the Sierra 18-8404-1 is sold as a single hex head bolt only; no nut or washer is included.

What thread class and direction does the 18-8404-1 use? It has a right-hand UNC thread with a Class 1A thread fit, standard for marine starter mounting hardware.

How many bolts come in an order? Each Sierra 18-8404-1 order includes one starter bolt; if two are needed for a starter, order two units.

What is the weight of the 18-8404-1 bolt? The Sierra 18-8404-1 weighs 0.1 pounds.

Is this a genuine Sierra part or an aftermarket copy? The 18-8404-1 is a genuine Sierra part, identified by Sierra part number 18-8404-1 and UPC 808282202125.

What head style does this bolt have for installation? The Sierra 18-8404-1 has a hex head, so it installs with a standard wrench or socket.

Can this bolt be used for other marine hardware applications, not just starters? The Sierra 18-8404-1 is marketed as a starter bolt, but because it is a standard 3/8-16 hex bolt of low carbon steel, it can be used anywhere that thread size and length are required.