Screws come in a variety of sizes and shapes. They also come with varying thread patterns that make them more or less suitable for use on certain materials. The correct type of screw for a particular project will ensure that it holds fast and stays in place. It can be confusing to choose the right screws for a job, especially when you’re working with multiple kinds of different screws, so it’s good to know some general guidelines.
There are two important numbers to know when selecting a screw: the screw gauge and its length. The first number, which is referred to as the screw’s major diameter, determines how wide or narrow the thread is. Screws with a major diameter smaller than 1/4″ are labeled in inches (for example, the screw size “8” corresponds to 0.164″) while screws with a larger major diameter are labeled in decimal fractions, such as 1/14″.
The second number, which is the screw’s thread count, indicates how many threads are on one inch of screw. Threads are measured by counting the peaks at the top of each groove, and combining that number with the screw’s major diameter will give you its size. For example, a screw size of “8” has a major diameter of 0.164″ and a thread pitch of 20 threads per inch.
Screws can be purchased in packs of varying quantities, so you should consider the number you will need for your project before purchasing them. Often, tradespeople will purchase in bulk to save money and reduce the number of trips needed to buy them. 1/4″ to mm