September 23, 2023

The correct fastener is critical to the success of any home improvement or construction project. For example, you wouldn’t hang a picture with a house nail or use upholstery tacks to build a table. Screws come in many varieties, and knowing how to select the right one can save time, money and frustration. It is also important to understand how the different types of screws are categorized and sized to help make the selection process more accurate.

The screw is a simple, versatile and efficient fastener that can be used in a wide variety of applications. It can hold wood together, bind metal parts and provide a tight seal in plumbing or electrical systems, and it is often used in the manufacture of automobiles and other consumer goods. However, the number of available screw sizes and types can be overwhelming for beginners and experts alike.

In this article, we’ll discuss the basics of US screws and provide some tips on how to correctly identify and select them for a particular application. We’ll cover everything from diameter and thread count to head type and length. We’ll also touch on the difference between imperial and metric screw sizes, as well as how to convert between them. Finally, we’ll examine the many different screw drive configurations such as slotted, Phillips, square, hex, and Robertson.

Before the advent of screw-cutting lathes in the 1770’s, it was impractical to mass produce screws with a consistent and accurate size. English instrument maker Jesse Ramsden invented the first satisfactory screw-cutting lathe, which inspired other inventors to create machines that would produce accurately sized screws on a larger scale.

Most modern screw threads are manufactured by cold rolling, where a cylindrical bar of steel is passed over a rotating die, which cuts the threads into the surface of the screw blank. This method provides a very precise thread with little or no excess material, and it can be accomplished with much faster speeds than the older hot-rolling method.

Regardless of the production method, all screws must be polished prior to threading to ensure they are smooth and free of burrs. After the threading operation, most screws are coated with a protective material to prevent corrosion and extend their service life. Screws that are exposed to the elements are frequently zinc-plated or black oxide-coated, and some are treated with other coatings to meet specific performance criteria.

Screws are commonly referred to by their diameter and length in the United States, with the latter usually represented as two numbers separated by a “x.” The first number, which is called the gauge, refers to the diameter – the larger the number, the greater the diameter. The second number is the length, which is typically expressed in inches.

The same numbering system is also used in metric screw threads, except that the diameter is expressed in millimeters and the pitch is indicated by appending the size of the thread in decimal form (e.g., M8x1).

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