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Machine Screws

Thread angles

  1. Unified threads have a 60 degree thread angle.
  2. BSW threads have a 55 degree thread angle.
  3. Unified threads and BS threads of the same pitch and diameter can be used interchangeably
    • 5-40 UNC can be interchanged with 1/8" BSW
    • 10-24 UNC can be interchanged with 3/16" BSW
    • 12-24 UNC can be interchanged with 7/32" BSW
    • etc etc

 Countersunk head angles

  1. Unified machine screws countersunk head angle is 80-82 degrees
  2. BS machine screws countersunk head angle is 90 degrees.
  3. Be very careful interchanging BS and Unified Countersunk and Raised head screws as problems can arise due to the resulting head shape difference.

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