One thing I quickly learned from my early days of working in a marine hardware store is that boats are held together not only with fiberglass and epoxy, but also with a multitude of different nuts, bolts, and screws—or fasteners, as I was instructed to call them. One of the most useful things to learn as a do-it-yourself boater is which ones are best for your specific project. Here's a list of the most popular to get you started.
Also known as “hex head bolts,” machine bolts are designed to be used in heavy-duty, through-bolt situations, such as in a hull to deck joint or mating an engine to its mounts. They come in various sizes based on diameter and thread count per inch. A lock nut or hex nut completes the assembly at the threaded end.
Machine screws are threaded along the entire length of the fastener and come with a variety of head choices; the most common are “oval head,” “flat head,” and “round head.” Generally used in through bolting applications, machine screws can also be used to screw into other materials that have been cut/tapped with the same thread, such as into an aluminum mast or a stainless winch plate. They are classified based on diameter and thread count per inch. A lock nut or hex nut completes the assembly at the threaded end.
Wood screws, as the name implies, are designed to be used to fasten wood to wood, and generally require a pre-drilled “starter” hole slightly smaller than their own diameter to work properly. They are sized by length and diameter and come with a variety of different head styles. If you’ve got a wooden boat with a wood deck, chances are your boat is filled with wood screws of one type or another. Otherwise, you might find them used belowdecks in wood cabinetry or trim.
Sometimes called a “sheet metal screw,” a self-tapping screw behaves exactly as the name implies: it bores its own path. A self-tapping screw is generally threaded along its entire length. Self-tapping screws are good all-purpose fasteners for use in applications where through-bolting isn’t required, such as installing light-duty hardware.
Hex nuts get their name from their six-sided shape. Designed to match a machine screw or machine bolt of the same thread count, hex nuts are used to mechanically tighten a stack of materials together.
Lock nuts are just like hex nuts, except that they are manufactured with an integral nylon insert that keeps the nut from backing off. Since most boats are vibration factories, it’s always a good idea to use lock nuts whenever the application allows.
As we mentioned earlier, this is a basic list. As you dig deeper into your boat, you’ll probably find all sorts of weird fasteners used for specialized applications.