Choosing the Right Screw

When you walk down the aisles at your local home store, do you ever wonder why they have so much shelf space filled up screws? I mean a screw is a screw, right? Sure, you need to have different lengths of screws, but how can there be a need for just so many different types of screws? Here's a quick overview of the most common types of screws as well as some idea of what they're used for. You'll see why your home store gives so much space to screws (and even then, they only stock the most common screw types).

Let's start with the basics:

Screws are used to attach two pieces of material together, because they have advantages over the next most logical choice -- nails.

Screws holds things together better than nails, but at the same time, they can be easily removed with little damage to the materials should you want to take something apart.

A screw can be reused over and over again.

Most screws are made out of steel, stainless steel or aluminum. They can also be chrome- or brass- plated, and you can even get specialized screws made out of other materials like nylon or plastic.

Bluing (it's actually black in color) is a finishing designed to prevent rusting. Galvanized screws (steel screws coated with zinc) are designed to prevent rust and are often used where metal and wood are being fastened together.

Head shape

Screws come with all kinds of different shaped heads. The different shapes are generally used for different applications. Here's a quick list of the most common head shapes.

Flathead (or countersink) screws have, not surprisingly, a head with a flat top. The head also has a tapered base that allows it to be driven flush with the surface when installed in a countersunk screw hole. This screw is most commonly used in furniture making where you want to be able to hide the screw head.

Pan head and oval head screws both have rounded sides, but the pan head is flat on top while an oval head has a rounded top and a tapered base that can be counter sunk. Both are often used for sheet metal work.

Round head screws are shaped almost like a half circle with a flat bottom. Even after it's been driven in, the head sits "proud" or above the surface. These screws are used to fasten material that is too thin to allow counter sinking and are often used in combination with a washer.

Head types

Not only are there different shaped screw heads, there are a number of common types of screw heads. While each type could be used for lots of application, they are commonly used for specific applications.

Straight (or slotted) heads are generally used for fastening simple joints, like fixing a faceplate to an electric outlet.

Phillips (or cross) heads are often used in appliances and other electronic equipment as well as woodworking and drywalling applications.

Robertson (square hole), Torx (five sided star shaped hole) and hex head (six sided hole) screws are often used in manufacturing, building and automotive applications. The shape of the head allows the screwdriver, drill driver or pneumatic tool to exert a lot of torque on the screw and drive it in tightly and securely.

Screw sizes

In addition to head type and head shape, screws are also classified by:

Their length in inches

How close their threads are together

Their size and thread gauge

The diameter of the screw shaft (not including threads)

Rated by numbers 2 to 24 -- the higher the number the larger the screw.

Figuring out what screw is right for you.

Choose the proper screw based on your application. You've got all kinds of possibilities, so choose the screw that has the head shape and characteristics to suit your project. For example if you're fixing your fence, you probably want deck or wood screws with a coating to prevent rusting and a tapered head that can sink below the wood surface. However, if you're attaching your gate hardware, you might want to use round or pan head screws with a Robertson shaped head so you can tighten the screw securely but still be able to move it if your gate shifts.

Choose the right length screw. The screw should pass completely through one board and into the other. You want to go as far into the second board as you can without having the screw protrude out the back end. For example, if you're fastening 1/2" boards together, a 1" screw would be good if you're fastening into an end while a 7/8" screw would be the proper choice if you're fastening into the side of the second board.

All this talk about screws, and we haven't come close to covering everything there is to know about them, nor mentioned other common screw types like lag bolts and dowel or gutter screws. Hopefully by now it's obvious why there are so many aisles with but screws at your home store.

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