In Australia, fasteners commonly come in two systems, or standards: the metric system and the imperial system. If you're working with fasteners, It’s useful to at least be aware of the existence of these systems. In this brief article, bought to you by Bolt-In Co Sunshine Coast, we review the metric and imperial systems and come to terms with some of their conventions, similarities & differences. Let’s go!

Why is There More than One System? 

There are multiple measurement systems used in different countries around the world. The metric and imperial systems are not unique to fasteners. They are the two main systems used to measure the distance and weight of.. everything! Here are some common conventions used by these two systems:

Kilometers (Metric) Vs Miles (Imperial)
Kilograms (Metric) Vs Pounds (Imperial)
Centimetres (Metric) Vs Inches (Imperial) 

The reason these are the two main fastener systems in use has interesting historical considerations. The imperial system originated in Britain and made its way to America. Meanwhile, the metric system originated in France. The metric system became more popular because it is simple and easy to use, and easy to convert (multiply or divide). However, because the imperial system had already been adopted by the USA, one of the world’s greatest economies and manufacturers, it continues to stay in use. This is despite the rest of the world mainly using the metric system. 

Are there any Other Fastener Systems? 

Yes. There are multiple systems. In Australia, the metric and imperial systems are the most commonly encountered systems. Internationally, there are also other systems such as Unified Thread Standard (UTS), British Standard Whitworth (BSW) and British Standard Fine (BSF), Japanese Industrial Standard (JIS), and ISO Metric Screw Thread.

How Imperial and Metric Fasteners different?

Generally, metric and imperial fasteners come in slightly different sizes. While fasteners of both systems are designed to solve similar problems, they go about it in different ways. For example, they use slightly different diameters (width of the fastener) and thread pitches (number of threads on the fastener). Metric and imperial fasteners are not interchangeable. 

Systems within Systems

An interesting aspect of the difference between metric and imperial fasteners are the terminology they ascribe to their thread pitches. In the imperial system, they use Unified National Fine Thread (UNF) and Unified National Course Thread (UNC) to describe their fine and course thread pitches. Meanwhile, the metric system uses Metric Course Thread (M) and Metric Fine Thread (MF) to describe this differentiation in the metric system. 

Which Should I Use: Metric or Imperial? 

The correct fastener to use will depend on the context of the application. For example, if you are replacing a fastener, ideally it will be replaced with a fastener of the same system and dimensions. Then you can be certain that the new fastener will have the correct capability for the job. In other situations the significance of the fastener system may not be as relevant - for example, when the fastener being used is independent of any other components.  

Otherwise, you can refer to the technical documentation for the project to determine the correct type of fastener to use. If you’re not sure, you are welcome to enquire with our team. In addition to supplying a wide range of stainless steel and high tensile fasteners on the Sunshine Coast, we also offer great customer service and a wealth of knowledge and experience in working with fasteners.