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BA - British Association

47.5 degree thread angle

Available in:
Chrome Alloy Steel for general purpose work
High Speed Steel,  precision ground, for more critical applications.

  • British Association - in 1884 the British Association for the Advancement of Science adopted a thread form and series, primarily for use in precision equipment.
  • It was inspired by one used in the Swiss watch and clock industry, and was formerly sometimes called the Swiss Small Screw Thread System; but is now just referred to as the BA series.
  • Like the Whitworth thread, it has a rounded root and crest, but the included angle is 47.5º.
  • Despite the date of origin and the British sponsorship, the BA is a metric series.
  • Not only is it based on the metre, but the thread frequency is specified in terms of round numbers in the pitch sequence, with threads per metre allowed to fall where it may.

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