If you were to take a look down any aisle filled with fasteners at a home improvement store, you would no doubt find your range of choices overwhelming. Anchors, eye bolts, machine screws, spring nuts, weld screws, and simple wood screws are just a few of the possibilities you have to choose from when looking at fasteners. While it would be impossible to review each of the different fasteners and their use, here are some basics.
When it comes to fasteners, there is one basic starting point: What kind of materials are you looking to fasten together? If the objects are both metal, then you want a fastener with machine threads. That basically means that all of the threads on metallic fasteners will be parallel with the head of the screw or bolt, whatever.
Now the threads on metallic screws or bolts come in two varieties: coarse or fine. Coarse-threaded fasteners will have a wider gap between each thread. And fine-threaded screws, well, have a small or “fine” gap between each thread. So which should you use? Well, it depends on the nature of the objects being fastened together. If a lot of force will be trying to pull the objects apart, then fine threads work better. The more threads the fastener has, the greater the force required to sheer the threads. Otherwise, coarse-threaded fasteners should be fine and they are generally less expensive anyway.
Wood fasteners are those with the winding corkscrew threads. The threads on wood screws begin at the very tip. That way, the fasteners will “bore” into the wood and hold the objects together better. Any fasteners that you see with the winding corkscrew threads are meant to be used with wood. However, there is an exception.
Known as self-tapping fasteners, some metallic screws will have hybrid threads that are a blend of the parallel and corkscrew threads. The corkscrew is not as pronounced on self-tapping screws nor do they extend out as far as those found on wood screws. Also, most self-tapping metallic fasteners are coated in a protective coating that helps them resist corrosion and rust. Self-tapping metallic screws are found all over your automobile and used primarily to hold body panels together. However, they have other applications as well.
So really, a real clue as the use and function of fasteners can be found from their threads. Still, there are hundreds, if not thousands, of different fasteners out there on the market to choose from. By knowing the differences between the threads, however, you should be able to choose a fastener for the job at hand that will work fine for you needs.