A machine screw is a unique type of fastener that’s threaded all the way through its entire length, unlike most other fasteners that have threading only at the top or bottom. Because of this, it can be inserted into holes that already exist in other pieces of equipment, rather than having to have them made for the screw when it’s purchased. This makes it important for anyone working with these kinds of screws to understand how they’re sized and what that means when searching for the right ones to use.
The first step to understanding machine screw size is knowing the number system that’s used to determine them. Most machines screws will have two numbers separated by a dash that indicate its diameter and threads per inch, or TPI. The first number represents the gauge of the screw, and the second one represents its diameter. The numbers aren’t the same for all fasteners, as some are based on imperial measurement systems and others are based on metric measurement systems.
While the majority of the world uses the metric system, most of America still uses the imperial system for measuring its screws. This means that, when you’re looking for a specific kind of screw, you’ll need to look at the gauge and diameter measurements to find the right one.
When shopping for a screw, you’ll also want to know the head type and style, since some can be used in different kinds of equipment and applications. The head style will influence the type of wrench or tool that you’ll need to use to tighten and loosen it. The style can also affect how much torque you can apply to the screw, and this will have a big impact on whether or not it’s suitable for your project.
Another factor to consider is the stress area of the screw, as this will determine how well it holds its ground against pressure. This will vary from coarse to fine screws, with the latter having a higher stress area than the former. Generally, coarse screws are better for applications that require heavy-duty gripping, while finer ones are better for lighter-duty jobs.
Measuring the thread pitch and diameter of a screw can be tricky, but it’s not impossible. The best way to do this is to use a thread gauge, which resembles a spark plug feeler and has multiple metal leaves with serrated edges designed to match the dimensions of standard machine screw threads. Basically, you hold the gauge against your screw, and you look at it under a light to see if there’s any light passing between the edge of the gauge and the top of the screw.
While it may take a bit of practice to get used to measuring machine screws, once you learn the basics, it becomes quite simple. You can then quickly find the perfect screws for your projects, saving time and frustration when trying to fit them into holes that aren’t quite wide enough. machine screw size chart