what screw size and thread measurements do we use?

OK this need some clarifying, what measurements do we use in Australia to size screws and fasteners?

Well it seems we don’t really know whether to go metric or imperial so strangely enough we’ve decided to adopt a policy of ‘making it up as we go along’, let me elaborate …

European and most metricated countries use fully metric sizing for all metric fasteners and fully imperial sizes for all non-metric, for example a 6 x 50 coach screw is 6mm thick by 50mm long, imperial fasteners are usually also available in primarily metric countries and an example size for a bolt would be say 1/2″ x 2″ BSW (this means 1/2 inch thick by 2 inches long and the thread type is British Standard Whitworth, very important to get the thread type right for bolts as theres lots of different types). OK that’s that, imperial or metric and never mixed.

The US is primarily imperial with very few metric fasteners in mainstream use and so sizing is given the same as the BSW example in fractions of inches followed by the type e.g UNC, UNF etc.  Wood screws are pretty much always imperial so that would be say, 10g x 3 1/2″ (which is 10 guage thick and 3 and a 1/2 inches long, guage is the imperial measure of shank thickness). So anything with a g in the diameter is imperial and should be followed by the imperial length. Metric fasteners are termed the same as European as in diameter x length and metric and imperial are never mixed.

So, in Australia we like to complicate matters by using combinations of metric and imperial for the same fasteners, for example common wood screws would be 10-12 x 40 or 8-15 x 20, 20, this actually means 8 guage diameter (imperial) x 20mm long (metric) and just to complicate matters further we chuck the thread pitch in there which is the 12 or 15 in the examples. Clearly in years gone by we couldn’t decide whether to go with European or American standards for our hardware and so have just made our own up, its also probably due to the the fact that most Australian fasteners are imported from different regions giving this wide mix of product, this can be seen in most fastener companies stocks where a full range (as some of ours is) is split into both imperial and metric.

and the confusion continues …

2 comments to what screw size and thread measurements do we use?

  • Jamie

    You would think something like screws would be the easiest part when it comes to construction. Ha, guess not. Before I took the OSHA 10 I was even more confused. But after their training I think I seem to have a grip on things better now.

    Thanks for posting the tips though!

  • Surely there is no justification for continued use of imperial fasteners and obsolete imperial terminology.
    I understand that Aust. manufactured machinery supplied with imperial fasteners can be rejected because it does not conform to Australian Standards and only complicates maintenance and stock keeping of spares. This is reason alone for buying from European suppliers in order to standardise production equipment.
    Why do hardware stores stock twice the stock (Imperial & Metric) that they need thus perpetuating obsolescence? It’s been 35 odd years now since the change to metric began, it’s time to finish it off and embrace the simplification it brings to all of us.

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