The Ultimate Guide to Marine Fasteners

Choosing the right fasteners for marine applications is a big deal, whether you’re maintaining a boat, working on a dock, or taking on an underwater construction project. Fasteners are what hold everything together, so it’s essential that they can stand up to the harsh, corrosive marine environment and not just any old nut, bolt, or screw from your local big box store will do. In this guide, we’ll explore what makes a fastener suitable for marine use, discuss various material options, go over the different types of fasteners available, and help you figure out which one is right for your needs.

What Makes a Fastener "Marine-Grade"?

Marine-grade fasteners are designed to resist corrosion and maintain their structural integrity when exposed to saltwater, moisture, and other environmental elements. Water, and specifically saltwater is highly corrosive to most metals, so it’s critical to use fasteners that can withstand the demands of this environment. The materials used in marine fasteners make all the difference in their durability and corrosion resistance. If you want your project to stay together then the alloy it is made from matters!

Alloys Matter!

The most common materials used for marine fasteners are stainless steel, silicon bronze, and monel. Each material has its advantages depending on your specific needs.

• 316 Stainless Steel: Alongside 304 stainless steel, 316ss is one of the

  

  more common alloys used for marine fasteners due to its superior corrosion resistance. The addition of molybdenum in 316 stainless steel provides extra protection against chlorides, making it ideal for use in saltwater environments. It will stave off rust and corrosion much longer than 304 stainless steel will, and it is only marginally more expensive.

• 304 Stainless Steel: While 304 stainless steel is also corrosion-resistant, it lacks molybdenum, which makes it less durable in saltwater conditions. For freshwater or less harsh environments, 304 stainless steel may suffice, but if you want the best protection, 316 stainless steel is the better option. Many places only stock 304 (which is also known as 18-8 or A2 stainless) and sell it as marine grade, but we don't think of it as a marine grade fastener here at Fair Wind. It is however easier to find and marginally less expensive if budget is a concern.

• Silicon Bronze: Historically, silicon bronze has been a favorite among wooden boatbuilders. This material has been used in wooden boats since as early as the 15th century and is still prized today for its excellent

  

  corrosion resistance, aesthetic appeal, and strength. It simply cannot rust due to the fact that it has no iron content in the alloy. Silicon bronze is especially popular in the wooden boatbuilding community because it works well with wood and does not cause staining or degradation over time. Its long history of use in wooden boat construction is a testament to its durability and reliability. It’s particularly valued for its strength and resistance to saltwater corrosion. Boatbuilders have relied on it for centuries and still do today. It's more expensive than 316 stainless steel, but also more corrosion resistant.

• Monel: This nickel-copper alloy is incredibly resistant to saltwater and acidic environments, making it ideal for specialized marine applications. Monel fasteners are typically used in more demanding or specialized applications where extra strength and resistance to corrosion are needed. However, it’s important to note that Monel fasteners tend to be extremely expensive and must usually be custom manufactured. They cost many multiples more than their silicon bronze equivalents but if money is no object then monel is a fantastic marine fastener alloy.

Each of these materials offers varying levels of corrosion resistance, but if you’re looking for long-lasting durability, availability, and reasonable pricing, 316 stainless steel or silicon bronze are typically the best choices.

316 vs. 304 Stainless Steel

As mentioned earlier, the primary difference between 316 and 304 stainless steel is the presence of molybdenum in 316. This additional element gives 316 stainless steel a significant advantage in resisting chloride corrosion, which is especially important in marine environments. While both grades of stainless steel are strong and corrosion-resistant, 316 is the superior option for saltwater applications.

If your project involves exposure to saltwater or high-chloride environments, 316 stainless steel is the clear choice. However, if your application is more general and won't be exposed to the harsh conditions of the sea, 304 stainless steel may offer an economical alternative.

Types of Marine Fasteners

There’s a wide variety of marine fasteners available, and choosing the right one depends on your specific needs. We specialize in only marine fasteners and have too many different types and sizes of nuts, bolts, screws, washers, and pins to mention them all (just browse our website!). But let’s take a closer look at just a few of the types of fasteners available from Fair Wind Fasteners:

• 316 Stainless Steel Hex Cap Screws: Also known as hex bolts, or just a "standard bolt" that you're used to seeing, these are perfect for heavy-duty applications. Whether you’re working on the hull or securing important components, hex cap screws offer the strength and corrosion resistance necessary to withstand the harsh marine environment.

• 316 Stainless Steel Socket Cap Screws: With a cylindrical head and Allen wrench drive, socket cap screws come with either a countersunk flat head, raised socket head, or an aesthetically appealing button head. We often see them in machinery that is exposed to saltwater or otherwise corrosive environments, as well as their frequent use on sailing yacht rigs or mounting deck hardware. The Allen or hex drive makes them easy to remove and replace if and when necessary.

• 316 Stainless Steel Carriage Bolts: Carriage bolts feature a rounded head with a square neck underneath that prevents rotation when tightened. They are ideal for wood-to-metal connections in marine settings, such as securing decking on a dock, attaching handrails, or securing deck fittings where access to one side of the fastener is limited. We see them quite a bit on chainplates.

• 316 Stainless Steel Lag Bolts: Also known as lag screws, these heavy-duty fasteners are used for wood applications. Their large threads provide strong holding power in wood, making them perfect for securing boat structures, docks, or other timber-based marine constructions.

• 316 Stainless Steel Flush Countersunk Washers: We developed them and had them made specifically for us here at Fair Wind due to seeing the need for a flush finish in certain applications. When used with a countersunk screw they give that flush appearance and also allow for the screw to be removed and replaced repeatedly over time without wearing out the material being fastened.

• 316 Stainless Steel Bonded EPDM Seal Washers: More resistant to aging than neoprene or similar materials, the EPDM bonded to our 316ss washers can seal out water and dampen vibrations. These are often found in roofing applications, but also come in handy in a lot of marine applications and are great for mounting machinery that vibrates or for sealing out corrosive saltwater. You won't find them in 316 Stainless anywhere else!

• Silicon Bronze Wood Screws: They differ from the wood screws that are commonly available in the fact that the threads are cut in place, and the unthreaded portion of the screw (the bodies) are just as wide as the outer diameter of the threads, therefore sealing out water once they are driven in. They are very common in wooden boat building, but somehow good quality is still hard to find. We carry more than anyone else, and keep them in stock in a flat head, oval head, or round head and with a slotted, frearson, or square drive.

• Silicon Bronze Clevis Pins: Often found on classic yacht rigging, clevis pins provide a secure connection and are finished with a corresponding bronze cotter pin. You'll find them on bronze turnbuckles or other hardware when a threaded fastener isn't the best choice.

• Silicon Bronze Hex Cap Screws: Just like their 316 Stainless equivalents mentioned above, they are often referred to simply as hex bolts and are great in a lot of similar applications. The bronze version can't rust of course, but is also used quite often in the electrical industry due to their high conductivity. You'll also find them in municipal water treatment centers, fastening high volume pumps in corrosive environments, and of course (our favorite here at Fair Wind) on boats!

• Silicon Bronze Machine Screws: Like any other machine screw, but in a highly corrosion resistant and rust free alloy. They're used on classic yachts to fasten deck hardware, but again due to bronze's high conductivity they can also be found in electrical applications. We have them with countersunk flat and oval heads, and also with a round (non-countersunk) head.

• Silicon Bronze Ring Shank Nails: We've already mentioned how bronze plays nicely with wood, so we of course have some great bronze nails for your woodworking projects. They'll never rust, and the rings on the shank will prevent them from pulling out of cupping or swelling timbers. We supply these often to deck builders, dock construction companies, and even a few companies for attaching house siding in coastal environments.

The Value of Silicon Bronze in Wooden Boatbuilding

As mentioned earlier, silicon bronze is an old world material used for marine fasteners, especially for wooden boats. Dating back to the 15th century, silicon bronze fasteners were used in wooden ship construction because of their exceptional corrosion resistance in saltwater and compatibility with wooden structures. The material doesn't cause staining or degradation of the wood over time, which makes it highly valued by wooden boatbuilders even today.

Fast forward to modern times, and silicon bronze is still prized for wooden boatbuilding and repair. Wooden boat enthusiasts and professionals continue to use silicon bronze fasteners for their excellent strength, long-lasting durability, and ability to maintain the integrity of the wood. While the material is more expensive than stainless steel, its unique benefits make it a worthwhile investment for anyone working with wood in a marine setting.

Choosing the Right Marine Fasteners

When selecting the best fasteners for your marine project, the key factors to consider are the material, application, and environment:

• Material: For many marine projects, 316 stainless steel offers a great compromise between strength, durability, availability, and price. If you’re working with wood, silicon bronze may be the better choice due to its compatibility with wooden structures and it's higher resistance to saltwater. For highly specialized projects with no budget, Monel might be worth considering but make sure to consider the lead time to get the custom manufacturing done. If custom manufacturing is what you need, we can do that too!

• Application: Different fasteners are better suited for different tasks. Hex cap screws and carriage bolts are excellent for heavy-duty applications, while socket cap screws offer more precision. For wood applications, lag bolts are a great option due to their strong holding power in timber. Using the best type of fastener for the application is just as important as choosing the right material that they are made of.

• Environment: Is the fastener going to be submerged in saltwater or in a damp, marine-adjacent environment? The exposure to saltwater or harsh elements will influence your choice between stainless steel, silicon bronze, or another material.

Maintenance and Longevity of Marine Fasteners

Even the best marine fasteners benefit from, maintenance to ensure they last as long as possible. Regularly inspecting your fasteners for signs of corrosion or wear is crucial, especially if they’re in constant contact with saltwater. If you notice any corrosion starting, replace the fastener before it fails and causes further damage to your boat or equipment.

Using an anti-seize compound such as our screw lubricant when installing marine fasteners can help prevent galling or seizing, both common issues in the marine environment where fasteners are exposed to moisture and salt.

Conclusion

Choosing the right marine fasteners is essential for ensuring the safety and longevity of your boat or marine project. At Fair Wind Fasteners, we offer a wide range of 316 stainless steel fasteners, as well as specialized options like silicon bronze for wooden boats. Whether you’re working on a small DIY project or a large commercial build, we’ve got the marine-grade fasteners you need to get the job done right and they're available by the piece or with deep bulk discounts for larger orders. We're trusted by DIYers, large corporations, and everything in between to provide quality marine fasteners that will hold up in challenging environments.