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Thread: Calculating UN thread minor diameter

  1. #1
    Associate Engineer
    Join Date
    Mar 2021

    Calculating UN thread minor diameter

    Hi guys,

    I've been looking for a formula to calculate the minor diameter section area for UN(UNC, UNF & UNEF) spec screws to calculate the area mentioned in Table 8.1.5 of MIL-HDBK-5J however none of the formulae mentioned in ASME B1.1 or Handbook H-28 seem to work. After scouting around online I came across the table provided here in EngineersEdge ( using the diameters mentioned in this table I was able to obtain the areas mentioned in MIL-HDBK-5J.

    Could someone from the EngineersEdge community provide me a set of equations to calculate the minor dia of UN spec threads from the nominal dia and thread TPI.


  2. #2
    Webpage has been updated to show thread graphics sufficient for an equation.

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