American screw sizes can be measured in a variety of ways, including the Unified Thread Standard (UTS), which was adopted in 1949 and includes fine thread UNF and coarse thread UNC variants. Screw sizes are typically described using two numbers, with the first indicating diameter and the second indicating threads per inch (TPI). For example, a #10 screw has a diameter of 0.190 inches or 4.826 mm. Conversion between imperial and metric measurements can be achieved through the use of formulas or conversion charts, which are available online and in reference materials. Understanding screw sizing is essential for selecting the appropriate screw for a project and ensuring compatibility with the material being fastened.

## American Screw Sizes in mm

Characteristics | Values |
---|---|

Description | The first number expresses the diameter, and the second is the number of threads per inch (TPI). |

Numbering | #0, #1, #2, #3, #4, #5, #6, #8, #10, #12, etc. |

Diameter | 4.826 mm (#10 screw) |

Thread Count | 32 (a #6 diameter screw) |

Length | 1 1/2" (a #6 diameter screw) |

## What You'll Learn

**#6-size screw**

**Understanding US Screw Sizes**

US screws come in a variety of sizes and measurements, which can be confusing when selecting the right one for a project. The numbers on screws, such as #6, refer to the diameter of the screw, with higher numbers indicating larger diameters.

A #6-size screw is a standard size used in various applications. It is part of the imperial system of measurements used in the US, which differs from the metric system used in most other parts of the world.

The #6 screw has a diameter that is roughly twice the size of its head. While there is no exact conversion, a 6-gauge screw typically corresponds to a head size of around 6 mm in the metric system.

**Applications of #6-Size Screw**

**Selecting the Right #6-Size Screw**

When choosing a #6-size screw, it is important to consider the length and gauge that best suit your project. The length of the screw refers to the portion buried in the wood or other material, excluding the head of a raised screw.

Additionally, screws with different acronyms offer various features. For example, ST (self-tapping) screws can be screwed into wood without a pilot hole, saving time, while ZP (zinc-plated) screws have a layer of protection against corrosion.

**Conversion and Measurement**

**To convert the imperial gauge of a #6-size screw to its metric diameter, you can use the formula:**

> Gauge = (Head diameter in sixteenths of an inch x 2) - 2

**For example, if the head diameter is 5/16 inch:**

> Gauge = (5/16 x 2) - 2 = 8

This calculation demonstrates the relationship between the imperial gauge and the metric diameter, which is approximately half the gauge value.

Understanding screw sizes, including the #6-size screw, is essential for any DIY enthusiast or professional. By knowing the specific features and applications of this screw size, you can make informed choices for your projects, ensuring the best results.

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**Screw gauges**

The gauge of a screw is also not directly related to the head size of the screw. It is a coincidence that, from screw gauges 6 and above, the gauge is close to twice the head diameter.

**The formula for calculating the gauge of an imperial screw is:**

**> (Head diameter in sixteenths of an inch x 2) – 2 = Gauge**

**For example, a screw with a head diameter of 5/16 of an inch would have a gauge of 8:**

> (5/16 x 2) – 2 = 8

There is no good system for converting gauge to a calibrated measurement, so it is best to consult a conversion table.

Screws have three basic measurements: gauge, threads per inch, and shaft length in inches. For example, a measurement of 6-32 x 1 1/2" means a #6 diameter, with 32 threads per inch, and an inch and a half long. When the middle number is absent, the screw has the "normal" number of threads per inch for that size and type of screw.

There are also metric screw gauges, which are measured in millimetres. The metric gauge roughly equals the screw head size in millimetres. For example, a 4 gauge screw will have a head that is approximately 4mm wide.

There are various tools available to help identify screw gauges, such as a screw thread gauge, which can quickly and accurately determine the size of a screw.

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**Screw measurements**

Screws are sized according to various measurement systems, depending on the region and industry. In the US, the Imperial system is commonly used, while the Metric system is prevalent internationally. Understanding screw measurements is essential for selecting the appropriate screw for a project and ensuring compatibility with the material being fastened.

**Imperial Screw Measurements**

Imperial screw sizes are determined by two numbers. The first number represents the gauge, which indicates the diameter of the screw. A higher number corresponds to a larger diameter. For example, a #6 screw has a larger diameter than a #4 screw. It's important to note that the head size of an imperial screw is not directly linked to its gauge.

The second number in imperial screw sizing refers to the length of the screw, excluding the head for raised or domed-headed screws. This length signifies how much of the screw will be buried in the material.

**Metric Screw Measurements**

In the metric system, screw sizes are denoted by the major diameter in millimetres. For instance, an M6 screw has a diameter of 6 millimetres at the threaded portion, excluding the head. The length of metric screws is also measured in millimetres, following the same convention as the imperial system.

**Conversion between Imperial and Metric**

Although manufacturers often provide both metric and imperial measurements on screw packaging, it's useful to understand the conversion between the two systems. The gauge (imperial) roughly corresponds to the screw head size in millimetres. Thus, a 4-gauge screw typically has a head approximately 4mm wide.

**To convert between imperial and metric measurements, a formula can be applied:**

Head diameter in sixteenths of an inch x 2) – 2 = Gauge. For example, a 5/16 head diameter multiplied by 2 equals 10, minus 2 equals a gauge of 8.

**Additional Screw Specifications**

Screws may also be classified by their thread type, which refers to the number of threads per inch. Standard screws have a "normal" number of threads, while some screws have a higher thread count, such as 32 threads per inch.

Furthermore, screws can have different types of heads, such as slotted, cross, Phillips, or pozidrive/supadrive heads. It's important to use the appropriate type of driver for the specific screw head to avoid slipping and damaging the screw head.

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**Metric and imperial screw sizes**

**Imperial Screw Sizes**

Imperial screw sizes are determined by two different numbers. The first is the gauge of the screw, which refers to the diameter. The larger the number, the larger the diameter. For example, a number 4 screw is much smaller than a number 12 screw. The second number is the length of the screw, which is given in inches. It is important to note that the length of a screw does not include the head of a raised or domed-headed screw.

**Metric Screw Sizes**

In the metric system, both the diameter and length of screws are measured in millimetres. The diameter of a metric screw is given as the number in millimetres, while the length is represented similarly in millimetres as well. For example, an M6 screw has a diameter of 6mm, while an M8 screw has a diameter of 8mm.

**Converting Between Metric and Imperial Screw Sizes**

Converting between metric and imperial screw sizes can be complicated, as there is no direct link between the head size of an imperial screw and its gauge. However, as a rough rule of thumb, the gauge of an imperial screw is approximately equal to the screw head size in millimetres. For example, a 4-gauge screw will have a head that is approximately 4mm wide.

**> (Head diameter in sixteenths x 2) - 2 = Gauge**

**For example, a screw with a head diameter of 5/16 inches would have a gauge of:**

> (5/16 x 2) - 2 = 8

So, the gauge of this screw would be 8.

**Acronyms and Abbreviations**

**There are several acronyms and abbreviations used to describe screws, such as:**

- ST – Self Tapping
- TFT – Twin Fine Thread
- ZP – Zinc Plated
- ZYP – Zinc and Yellow Passivated

In conclusion, understanding screw sizes can be challenging, especially when converting between metric and imperial measurements. It is important to know the basics of screw sizing, including the diameter and length, to ensure that you select the right screw for your project.

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**Screw thread**

A screw thread is a helical structure that enables the conversion of rotational and linear movement or force. It is the essential feature of a screw, both as a simple machine and as a threaded fastener. The mechanical advantage of a screw thread depends on its lead, which is the linear distance travelled by the screw in one revolution.

- External thread/Male thread: Found on the outside of a screw or bolt.
- Internal thread/Female thread: Found on the inner surface of a hollow cylinder, such as a cap or nut.
- Thread angle: The angle between the thread flanks.
- Major diameter: The largest diameter of the screw.
- Minor diameter: The lower extreme diameter of the thread.
- Pitch: The distance from a point on the screw thread to the same point on the next thread.

**Determining Screw Thread Size**

The size of a screw thread refers to its dimensions and is crucial for ensuring a stable and secure connection. There are two main systems for measuring screw thread sizes: the Unified Thread Standard (UTS) and the metric system.

**Unified Thread Standard (UTS)**

The UTS uses an inch-based measurement system and includes different thread series, such as the coarse thread series (UNC) and the fine thread series (UNF), which are finer, tighter threads. Threads are measured in threads per inch (TPI). To determine the screw size, you need to count the number of thread peaks along a one-inch length and measure the major diameter of the screw. For example, if the major diameter is 1/4" and there are 20 TPI, the screw size is 1/4" x 20.

**Metric System**

The metric system uses millimetres (mm) to measure screw thread sizes. To determine the screw size, you need to measure the major diameter and the thread pitch, which is the distance between two adjacent thread peaks. For example, a screw with a major diameter of 6mm (represented as M6) and a pitch of 1mm would have a size of M6 x 1mm.

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**Frequently asked questions**

The first number refers to the diameter of the screw, and the second is the number of threads per inch (TPI). For example, a #10 screw has a diameter of 0.190 inches or 4.826 mm.

Use a digital caliper to measure the diameter and length. Refer to conversion charts to find equivalent sizes if needed.

Imperial screw sizes are determined by the gauge and length of the screw. The larger the gauge number, the larger the diameter. Metric screws are measured in millimetres for both diameter and length.

The most common types of fasteners used in construction include screws, bolts, nuts, washers, and anchors. Each type serves specific purposes based on load-bearing capacity, material compatibility, and environmental conditions.

Larger diameter fasteners generally have higher load-bearing capacities due to increased surface area and strength. Refer to load charts or consult engineering specifications for precise calculations.