Understanding Machine Screw Hole Sizes For Number 12 Screws

number 12 machine screw hole size

Machine screws are used in a wide range of applications, from construction and manufacturing to industrial and production environments. The measurements of machine screws follow the Unified Thread Standard (UTS) and the ISO metric screw thread system. While the metric system is used across the world, the United States follows the ASME/ANSI standard under the UTS, with measurements in inches. The #12 machine screw hole size is just under 1/4 of an inch in diameter.

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The #12 screw is slightly under 1/4 inch in diameter

When it comes to screw sizes, there are two main systems of measurement: the Unified Thread Standard (UTS) and the ISO metric screw thread system. The former is used in the United States, while the latter is used in the rest of the world.

In the UTS system, the #12 screw is just under 1/4 inch in diameter, falling within the range of screw sizes that are labelled from gauge #0 to gauge #12. This is because all machine screws with an outside diameter under 1/4" fall within this range.

The #12 screw's precise diameter in inches is 0.216", which is slightly less than 7/32 inches (5.6mm). This measurement is important when identifying the screw size, as the "12" in 12-24 does not refer to the screw's diameter but is instead a size designator with no numerical meaning.

The 12-24 screw type is commonly seen in pre-threaded racks, with fasteners that are slightly larger than those found on 10-32 screws. The 12-24 screw has 24 threads per inch, which is a higher thread count than the coarser 10-32 screw type.

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The Unified Thread Standard (UTS) is used for American screw sizes

The Unified Thread Standard (UTS) is a standard for screw threads commonly used in the United States and Canada. It defines the thread form, allowances, tolerances, and designations for bolts, nuts, and other threaded fasteners. The UTS is controlled by the ASME/ANSI in the United States and is the North American equivalent of the ISO metric thread system.

UTS threads have a 60° profile, similar to the ISO metric screw thread, but the characteristic dimensions of each UTS thread, namely the outer diameter and pitch, are chosen as inch fractions rather than millimeter values. This is a key distinction between the UTS and the ISO metric system.

The standard designation for a UTS thread consists of a number indicating the nominal (major) diameter of the thread, followed by the pitch measured in threads per inch (TPI). For diameters smaller than 1/4 inch, the diameter is indicated by an integer number from #0 to #12, with each number representing a specific diameter. For example, a #12 screw has a major diameter of 0.2160 inches. Above 1/4 inch, the diameters are given in inch fractions, such as 1/4", 3/4", or 1 1/4".

The UTS includes different series, such as UNC (coarse), UNF (fine), and UNEF (extra fine), which define specific diameter and pitch combinations. The class of a UTS thread is also specified, with codes like 1A, 2A, or 3A for external threads, and 1B, 2B, or 3B for internal threads. The first character of the code indicates the fit, with 3 being a tight fit, 2 a medium fit, and 1 a loose fit.

The UTS is commonly used for rack screws in server equipment. For example, the 12-24 thread type, which indicates 12 as the size designator and 24 threads per inch, is commonly used for pre-threaded racks and has a diameter of slightly less than 7/32 inches (5.6 mm).

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The ISO metric screw thread system is used for the rest of the world

The ISO metric screw thread system, also known as "M" series threads, is the most commonly used screw thread system worldwide. It was one of the first international standards agreed upon when the International Organization for Standardization (ISO) was established in 1947.

The "M" designation for metric screws indicates the nominal outer diameter of the screw thread in millimetres. For example, an M6 screw has a nominal outer diameter of 6 millimetres and will fit well in a 6 mm drilled hole. The standard metric rack screw is called M6 x 1, where "M" indicates it's metric, "6" is the outer diameter in millimetres, and "1" is the distance between adjacent threads.

The design principles of ISO general-purpose metric screw threads are defined in international standard ISO 68-1. Each thread is characterised by its major diameter and its pitch. The ISO metric threads consist of a symmetric V-shaped thread with a 60-degree angle between the flanks of the V. The thread depth is calculated as 0.54125 times the pitch.

Metric fasteners are specified with a thread pitch instead of a thread count. The thread pitch refers to the distance between threads, expressed in millimetres. Coarse pitch threads are the most common type and are identified by their diameter. Fine pitch threads, on the other hand, are less common and are identified by their diameter and pitch size.

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The term 12-24 refers to 24 threads per inch

The term "12-24" refers to 24 threads per inch and is one of the most common types of rack screws used to attach equipment to the vertical uprights of a 19" rack. The term originates from the Unified and American Screw Threads for Bolts, Nuts, and Machine Screws standards published by ANSI B1.1-1974.

In the term "12-24", the number "12" is a size designator with no numerical meaning, while the number "24" refers to the 24 threads per inch. 12-24 rack screws are more commonly found in pre-threaded racks, and their fasteners are slightly larger than those of 10-32 screws, with more course threads. The diameter of a 12-24 screw is slightly less than 7/32 inches or 5.6mm.

When compared to 10-32 screws, which have a diameter of 3/16" (4.8mm), 12-24 screws are larger and have a diameter of 7/32" (5.6mm). This makes them more suitable for use with most racks, while 10-32 screws are typically used with Dell equipment and audio racks.

The main difference between 10-32 and 12-24 threads lies in their dimensions. While both types are commonly used in racking equipment, the larger size of 12-24 threads makes them more suitable for most racks. On the other hand, 10-32 threads are more specific to Dell equipment and audio racks. Therefore, when selecting screws for racking equipment, it is important to consider the compatibility of the screw thread type with the equipment being used.

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The number 12 has no numerical meaning

The "24" in "12-24" refers to the number of threads per inch. This screw type is commonly found in pre-threaded racks and has a diameter of slightly less than 7/32 inches (5.6mm). It is larger than the 10-32 screw type, which has a diameter of 3/16 inches (4.8mm).

The Unified and American Screw Threads for Bolts, Nuts, and Machine Screws standards published by ANSI B1.1 in 1974 are the source of the 12-24 designation. While there is no universal standard for server rack screw threads, 12-24, 10-32, and M6 are the three types that are most commonly used.

Frequently asked questions

The #12 machine screw has a diameter of just under 1/4 inch.

The #12-24 screw is slightly larger and has a diameter of 7/32 inches (5.6mm), whereas the #10-32 screw has a diameter of 3/16 inches (4.8mm).

The standard measurement system depends on your location. In the United States, machine screw sizes are typically given in inches according to the Unified Thread Standard (UTS). In the rest of the world, the ISO metric system is used, with sizes measured in millimeters.

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