Here is a list of all the postings Stephen Wallin has made in our forums. Click on a thread name to jump to the thread.
Thread: BA Threads or Metric Threads? |
16/07/2009 20:14:59 |
I am a spot suprised that BA are widely proposed for engineering models, as the ME series, based on Whitworth thread forms, is usually more accurate than BA. Most metric pitches are a bit too course for the diameter for model use, even with the fine pitch series.
It was mentioned that BA are Imperial, but that not quite right as the base used is metric, and of Victorian origin.
The published tables may be quoted in Imperial sizes, usual thousanths, for the smaller sizes, but the No0 was deliberately started at a metric size.
I worked in instrument making, and BA is still widely used, and a very useful system for smaller sizes especially below 12BA and on to 20BA, (a bit smaller than metric .5mm).
They were instrument threads, giving a fine pitch for secure nuts and fastenings, and are not a model of an actual Whitworth etc, which have a different faced angle etc, and for each size have fewer TPI.
There is nothing against substituting metric for Imperial etc., as appropriate, but where appearnce matters ME works.
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