Selecting a suitable fastener for a task is never about size and material alone but about thread types as well. For professionals in Australia’s construction or trades sectors, it is important to know how to differentiate between metric and imperial threads. Getting this wrong will result in stripped threads, poor connectivity, and delayed tasks. This guide will take you through the principal differences between metric and imperial systems to enable you to make a suitable fastener choice all the time.
Understanding Thread Types
Threads are twisted ridges found upon a screw, nut, or bolt. The particular appearance of these threads – the diameter, pitch, and angle – will dictate how fasteners will fit into one another. There are two most common thread standards employed nowadays internationally: metric and imperial.
Though Australia made metric its only system of measurement in the 1970s, businesses will still have to contend with imperial fasteners when dealing with older structures or when dealing with machines which originally originated from countries such as the United States. Comprehensive knowledge of two systems is therefore required in day-to-day operation.
Metric Threads Standards
Metric threads are Australia and world standards. They are quickly identifiable by their “M” designation, to which are added numbers that denote the fastener’s properties.
How to Read Metric Threads Designations
The identification of a metric thread is a plain, uncluttered indication. A bolt that is marked as an M8 x 1.25 is no problem to interpret. The “M” is a sure indicator that it is a metric thread, the “8” tells us that the nominal diameter is 8 millimetres, and the “1.25” is the pitch – the distance between threads – also in millimetres. When no pitch is given, it is assumed to be a “coarse” thread of standard pitch for that diameter.
Advantages of Metric Threads
The greatest advantage of the metric system is that it is easy to use and is generally universal. As measurements all work from millimetres down, calculations make complete sense and are easy to complete. This is why accessing metric fasteners as well as suitable tools all across Australia and internationally is a relatively simple feat to achieve, giving most users consistency and accessibility.
Imperial Thread Standards
Imperial threads that are also referred to as Unified Thread Standard (UTS) are common in the United States. These are standards including UNC (Unified National Coarse) and UNF (Unified National Fine).
How to Read Imperial Thread Designs
Imperial thread terms are a bit more involved. An example of a standard imperial size would be 1/4″-20 UNC. “1/4″” is the major diameter expressed in inches. “20” is the Threads Per Inch (TPI) and denotes that there are 20 threads per one inch of fastener material length. “UNC” is the designation to indicate thread series, which in this example is Unified National Coarse.
Notice this is different from a direct pitch measurement found in a thread term of metric layout. You have to count threads across a predetermined distance in the imperial system.
Advantages of Imperial Threads
Although less frequent in new Australian construction, there is a role for imperial fasteners. Coarse thread imperial bolt (UNC) is frequently used where rapid disassembly and assembly are desired, as it is quicker to fasten due to its higher thread angle. They are also marginally less sensitive to thread damage. Knowledge of imperial standards is important where American-made gear needs to be dealt with or older jobs where metric parts just will not fit.
Selection of Correct Fastener
It is critical that tradespeople appreciate the difference between metric and imperial thread systems, and you’ll then understand the products at Bricon Industries and beyond. Metric provides a simple decimal-based system that is used as an internationally agreed standard, whilst the imperial is retained to a limited degree in specific usage and industry.
Always check necessary specifications of your work to allow you to choose a fastener that will provide a safe and sure joining. Getting it right from the start will save time and money and assist in maintaining the integrity of your work!
