Screws and Bolts

Popular Mechanics Senior Editor Roy Berendson shares a quick tutorial on fasteners. According to Roy, here is a list of the seven most common types of screws and bolts that every homeowner will come across at some point in their lives.
Hex bolts or hex head screws are large hex bolts (hex!), used to fasten wood to wood or metal to wood. “Unlike carriage bolts, they tend to spin when you tighten them, so you need to hold the head of the bolt with a wrench or socket and then use a second wrench to tighten (or loosen) the nut,” Roy said. . Hex bolts have small threads and smooth shank and are available in steel or stainless steel for interior use or galvanized steel for exterior use.
Wood screws have a threaded rod used to fasten wood to wood. These screws can have different thread lengths. When tightening soft woods like pine and spruce, Roy says it’s best to use screws with fewer threads per inch. On the other hand, fine threaded screws should be used when fastening hardwoods. There are many different types of wood screw heads, but the most common are round and flat. “The head of a round head screw is completely above the workpiece. The head of a flat head screw is embedded in the workpiece,” explains Roy. Wood screws can be plain steel, brass, stainless steel, or steel with a weather-resistant surface.
Sheet metal screws are used to fasten two pieces of sheet metal together or to connect sheet metal to other types of metal such as pipes. These screws usually have a round, flat or even hex head. The thing to remember about sheet metal screws, Roy says, is that they are for threading. “The tip of the screw is shaped to cut a thread in the host metal where the screw is driven,” he explained, adding that they are often referred to as self-tapping screws. They almost always use plain steel, weather-coated plain steel, aluminum, or stainless steel for maximum weather resistance.
Machine screws are a mixture of small bolts and screws used to fasten metal to metal or metal to plastic. In homes, they are used to protect electrical components, such as connecting lamps to electrical boxes. In such an application, the machine screw becomes a hole into which the corresponding thread is tapped or “tapped”. Mounting screws need a nut if the hole is not threaded, says Roy.
A socket head screw is a machine screw with a socket head into which a hex key is inserted. In most cases, these screws are used to join metal to metal and require a tight fit to ensure a secure connection. They are often used when items are likely to be taken apart and reassembled over time.
Lag bolts, more commonly known as lag screws, are usually large in diameter and long enough to penetrate deep into the wood and create a strong connection with little chance of loosening the screw once tightened. Common places to find propellers of this type are decks, docks, and wooden retaining walls. Because pressure-treated exterior wood is corrosive, the screws are treated with an anti-corrosion coating. “They are hot-dip galvanized or made of stainless steel,” explains Roy.
A carriage bolt, which can be considered the lag screw’s cousin, is a large bolt used with washers and nuts to hold thick wood blocks together. Beneath the round head of the bolt is a cube-shaped extension that cuts into the wood and prevents the bolt from turning when the nut is tightened. This makes it easier to turn the nut (you don’t have to hold the head of the bolt with a wrench) and prevents unauthorized access. “The nut is almost always on the back of the assembly. Thus, once tightened, the fastener cannot be easily loosened because the head of the carriage bolt is rounded – like an old-fashioned rivet – pliers cannot do this. that or a wrench,” Roy explained.