14 Mar 2012

Sizing Screws

Posted by bcsands

At BC Sands we have no less than three aisles containing a bewildering array of ‘fasteners’.

‘Fasteners’ is a handy catch-all phrase for screws, nails, bolts, plugs, anchors, fixings – essentially almost anything that can attach something to something else. While some types of fastening can be used in different circumstances, many are designed to be the perfect type, shape, size and material for a highly specific purpose. Sadly this article is too short to discuss this in much detail – it would take an entire book. However, there is one aspect of fasteners that can be confusing in Australia and that is understanding the sizing.

Sizing is confusing, because as well as manufacturing our own fasteners, we also import from Europe and America. Like Australia, Europe is largely metric, which means most European countries use centimeters to specify sizing.  Americans, on the other hand, use imperial measurements for almost everything – which means feet and inches. While fasteners with imperial measurements are also available in metric countries in Europe, the same is seldom true of America.

This probably wouldn’t be a problem if everybody specified the measurements they were using – but that doesn’t always happen. . All too often, a size is given in numbers with no helpful ‘mm’ or ‘ ” ‘ symbol to help you (‘ ” ‘ means inches), and if you are not instantly familiar with the world of screw sizes, it’s likely that you will have no idea of just what you are ordering.

So when you are confronted by a screw that is, for example, 8 x 25 – how can you know how big that actually is?!  If you are standing in a store comparing the sizes of fasteners you can probably figure it out. But it can be tricky if you are trying to order by phone or online. However, there are a few clues that can help you understand the measurements

One thing that is usually consistent is the use of ‘gauge’ to measure the diameter (thickness) of a screw. This is usually signified by a ‘g’, e.g. 8g. Conventionally the first number is a screw measurement is the gauge. So in the example above, the ’8′ refers to the diameter of the screw. Gauge is a standard measurement, but conversion charts are available if it’s important to know the measurement in mm – in this case 8g is roughly equivalent to 4.2mm.

The second figure in our 8 x 25 screw refers to the length – in this case 25mm.

How do I know that the 25 is mm? The fact that this is a whole number is my clue. Inches are big compared with centimeters/millimeters, so you will often find that these measurements are smaller and they will also often involve fractions, e.g. 1/2 x 6  would mean a screw with a gauge of 6 that was 1/2  an inch in length, and 1 x 8 would mean a screw with a gauge of 8 that is 1 inch in length.

The one consistent aspect of this is that imperial and metric measurements are not mixed on a single item – thankfully. This is particularly helpful for larger screws where gauge is no longer used and they are specified in millimetres or inches.

As for head types, thread types and pitch, such as BSW, UTS, BA well, let’s leave that for another day…



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