When you work with international suppliers, parts from different countries or various technical specifications, you quickly come across different standards. 

In Europe, millimeters (mm) are usually used, while many American and British manufacturers still use inches (").

In order to compare parts correctly and to copy specifications flawlessly, it is important to be able to easily convert thread sizes from millimeters to inches and vice versa.

What are wire sizes?

A wire size refers to the diameter (ø) of a wire and is measured in millimeters or inches. It is an important specification when selecting screws, bolts, nuts, and other mechanical parts.

 

Historically, the length of the human thumb was used as a reference measure. One inch was equal to the width to the top phalanx of an adult male, which was then divided into smaller units for "accurate measurements". 

 

After the introduction of the metric system, the "thumb" was officially equated to a centimeter in 1860. In English-speaking countries, they use inches as the measure of length. One inch equals 25.4 mm

 

Converting from millimeters to inches

Converting wire sizes is easy with a fixed formula. The ratio of metric to imperial units is equal: 1 inch = 25.4 millimeters

 

The formula to convert millimeters to inches:

 

Inches = millimeters ÷ 25.4

 

Example:
A wire with a diameter of 12.7 mm is exactly 0.5 inches.

 

Correctly measuring wire sizes

In addition to being able to convert wire sizes, it is also important to know how to measure wire sizes accurately. Below are some useful tips for measuring both internal and external threads: 

• Use a caliper or wire gauge to precisely determine the diameter of the wire.

• Measure the outer diameter (ø) for male thread and the inner diameter (ø) for female thread.

• Check your measurements multiple times to ensure accuracy.

With the right knowledge and tools, you can easily measure and convert wire sizes.

 

Types of thread types and how to choose the right type?

When working with thread sizes, you often come across specific thread types, such as 

• G threads, also known as BSPP (British Standard Parallel Pipe), are straight, which means that the diameter remains the same throughout the entire length.

• R thread, also known as BSPT (British Standard Tapered Pipe), is tapered.

• NPT thread, National (American) Pipe Thread Tapered, is tapered. The male and female threads become narrower towards the end.  

• UNF threads, which stands for Unified National Fine, are cylindrical and have more thread revolutions per inch.

It is the difference between BSP and NPT threads?

The biggest difference between British Standard Pipe (BSP) and National Pipe Taper (NPT) threads lies in the angle of the V-profile:

• BSP (Gas Thread): Uses a 55° threaded angle

• NPT: Uses a thread angle of 60° 

While both types of threads are similar and similar in quality, they are not interchangeable. The angular deviation ensures that a correct and leak-free seal is not formed, even with the help of sealants.

 

The BSP sizes often indicate the inside diameter of the pipe and not the actual diameter of the wire, which can cause confusion when converting. Therefore, it is important to use the correct conversion tables when working with these sizes.

 

Refer to our wire size conversion chart to compare millimeters and inches.

 

Quickly and easily find the right size for your application?

Feel free to contact us and we will be happy to help you with the best solution for your project.

 

 

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