When you buy a case for assembling a new PC it comes with several screws and other small components. Even seasoned technicians have trouble in telling what is the exact use of each screw that comes with the PC case. In this tutorial we will present a detailed explanation about all screws used on a PC and when to use each one of them, so by reading this tutorial you will enhance your PC assembling skills.

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Figure 1: So many different screw types are used on the PC. What a mess!

The screws vary in three aspects: their thread, the shape of their head and their length. The length and especially the shape of their head can vary a lot, but there are only three types of thread used on the PC. So we think the best way to classify the screws found on a PC is thru their thread. On Figure 2 you can see these three thread types.

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Figure 2: Types of thread found on PC screws.

The first thread type, shown on the left hand side from Figure 2, is a self-tapping screw used to fasten fans to the case (and also ventilation-related plastic parts like ducts, if your case has them). That is the only use of this kind of screw in the whole PC, so it is pretty easy to identify this kind of screw. This screw is usually 10-mm long and usually has a flat-head, like shown on Figure 3, and its head is cut to accept a #2 Phillips screwdriver.

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Figure 3: Screws used to fasten fans and ducts to the PC case.

The second thread type found on screws used on the PC uses UNC (United National Coarse) 6-32 standard, which means a thread using a #6 wire (0.1380”-diameter wire) with 32 threads per inch (0.0313” pitch). They are cut to accept a #2 Phillips screwdriver. To simplify, let’s call this thread as “thick thread” from now on, as the third thread type is thinner than this one.

The third thread type found on screws used on the PC uses M3x0.5 standard, which is a standard set by ISO using the metric system. It means the use of a 3-mm wire with a 0.5-mm thread pitch. They are cut to accept a #1 Phillips screwdriver. To simplify, let’s call this thread as “thin thread” from now on, as it is thinner than the other types of thread used by PC screws.

Screws using both thin- and thick-thread can be found using several different types of heads and several different lengths, and here is where most people get confused. So let’s talk deeply about all screws found on a PC.