How to Understand Common Screws

We see screws every day of our lives and like most common things, never really think about them. When you do think about it, the world of screws can actually be quite complicated, since they come in all kinds of shapes, sizes and are made from lots of different materials designed to do different jobs. Here's a basic overview of screws, how to understand some of the differences between them and hopefully choose the right screw for any particular job.

Things You'll Need

• An understanding of different head shapes
• An Understanding of why screws are made from different materials
• An understanding of different screw head types

Instructions

1. Consider that screws are better for holding things than nails. Screws are easy to install, but perhaps more important, easy to remove without damaging the surrounding material. Plus, screws have an added advantage in that they can be reused.

2. Understand that screws are classified according to their length (in inches), their size and thread gauge rated by numbers 2 to 24 (the higher the number, the larger the screw).

3. Screws are made from many different materials. Most commonly, screws are made from steel, aluminum or stainless steel. Specialty screws can be made with chrome or brass plating. Galvanized screws (steel screws coated with zinc) or screws with bluing applied to the surface are designed to prevent rusting.

4. Consider some different head shapes:
   
   • Flathead or counter sink screws have a head with a flat top and a tapered base designed to be driven flush with the surface when installed in a counter sunk screw hole. They are commonly used in furniture manufacture.
   
   • Pan head and oval head screws both have rounded sides, but the pan head is flat on top while the oval head has a rounded top. Both types are commonly used in sheet metal work.
   
   • Round heads have a top that is rounded on top. These are often used in combination with a washer on material that is too thin to be counter sunk.

5. Learn screw head types:
   
   • Straight (or slotted) screw heads are usually used for simple fastening such as a faceplate to an electrical outlet. Since a screwdriver can easily slip out of the slot and mar the work surface, they aren't often used in woodworking.
   
   • Phillips (or cross-shaped) are often used in electrical equipment, woodworking and drywall applications.
   
   • Robertson (square hole), Torx (five-sided star shaped) and hex head (six-sided) screws are commonly used in building and manufacturing applications. The head shape allows the screwdriver to apply a lot of force and drive the screw in tightly and securely.

Tips & Warnings

• Choose the screw with the proper head shape and characteristics required for your job. Slotted screws are usually harder to install and remove than either Phillips or Robertson heads. Also, choose the head shape that best suits your project. Round heads will sit up above the surface of the material, while flathead and even pan heads can be countersunk.

• Use the proper length screw as well. You want the screw to penetrate and hold in the underlying piece of material, but you don't want it to protrude so far its tip will be visible or even bubble the surface.