The following content mainly talks about screw and the two popular hard drive screws, #6-32 UNC screw and M3 screw. Read more similar information on MiniTool Partition Wizard official site.

A screw is a kind of fastener, which was typically made of metal and was characterized by a helical ridge (female thread/internal thread). It is used to fasten materials by engaging the screw thread with a similar female thread (internal thread) in the matching part.

Screws are often self-threading or self-tapping. When the thread cuts into the material when the screw is turned, it creates an internal thread that helps put fastened materials together while avoiding pull-out. Besides metal screws, there are also wooden and plastic screws.

Tip: A bolt has a similar shape, function, and fastening mechanism to a screw.

What Are Hard Drive Screws?

Here, hard drive screws usually refer to screws for fastening physical hard disk drives onto the computer host cases. Or, they can also be used to fasten the inner components of a hard disk into drive cases.

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Common Types of Hard Drive Screws

There are thread standards define preferred size combinations that are based on generic units, some on the inch while others on the millimeter (mm). Those standards include the Unified Thread Standard (UTS) originating from the United States and the world-standardized ISO metric screw thread.

#6-32 UNC Screw

The #6-32 UNC hard drive screw is a UTS screw. It specifies a major thread diameter of #6, which is defined as 3.51 mm (0.1380 inches) and 32 threads per inch (tpi) that is equal to a thread pitch of 0.7938 millimeters (0.031250 in). The optional UNC specification shows that the standard coarse thread is used, which is defined for #6 screws, as 32 tpi rendering “UNC” redundant. Yet, it may be seen when other specifications (plating or other treatments) are also specified.

#6-32 UNC HDD screws are the most common screws by far found inside of computer cases. Their most popular lengths are 3/16 inches (0.1875 inches, 4.76 mm) and ¼ inches (0.25”, 6.4 mm). The less common length is 5/16 in (0.3125 inches, 7.94 mm). There are also non-standard metricized hard drive screw sizes like 1/5 inches (0.20 inches, 5 millimeters).

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The #6-32 UNC hard drive screws are used for the below purposes:

  • Fastening a 3.5” hard drive to desktop host case
  • Keeping an expansion card in place by its metal slot cover
  • Securing a power supply to the case
  • Connecting case components to one another
  • Fastening case main cover

M3 Screw

The M3 hard drive screw is a metric screw specifying a nominal diameter of 0.12 inches (3.00 mm). Its standard coarse thread pitch is defined as 1/50 in (0.20 inches, 0.5 mm). The M3 screw is the second most popular screw used in computers. Its sizes range from 1 to 20 millimeters in length. The following are the common functions of M3 SSD screws:

#6-32 UNC Screw vs M3 Screw

As a thicker screw with a coarse thread, the #6-32 UNC hard drive screws are more appropriate for securing larger computer components and thicker materials, which require increased holding strength. The large size and coarse thread of #6-32 UNC hard drive mounting screws make them easier to operate with during assembly, and with less risk of cross-threading.

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Also, the integrated flange of a #6-32 UNC hard drive screw offers greater holding strength with less risk of pull through; the hex head makes it easier to work with during assembly with powered torque screwdrivers.

While the M3 hard drive screw is a thinner screw with finer thread than a #6-32 UNC screw. This makes it more appropriate for securing into smaller case components and thinner materials, which requires good strength in a limited space. The size and fine thread of an M3 screw make it suitable for situations where a #6-32 UNC hard drive screw would be too large. 

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