{
  "id": "thread-multipliers",
  "source": "https://ctrlplanner.com/walkback",
  "license": "CC-BY-4.0",
  "attribution": "ctrlPlanner, https://ctrlplanner.com/walkback",
  "title": "Pitch diameter shift per unit of coating thickness, by thread flank angle",
  "standard": [
    "MIL-STD-870",
    "Federal Screw Thread Specification H28"
  ],
  "description": "A coating sits normal to the thread flank, so it shifts pitch diameter further than it shifts a flat diameter. For a 60 degree thread the shift is about four times the per-side thickness, against two times for a diameter. Shallower flanks shift further.",
  "method": "sidedness * 2 * tan(30 degrees) / tan(angle / 2). Sidedness is 2 for a both-sided feature and 1 for one-sided.",
  "diameterReference": {
    "pitchDiameterShiftPerSide": 2,
    "note": "A both-sided plain diameter moves by twice the per-side thickness. Every thread row below is the same figure with the flank correction applied."
  },
  "rows": [
    {
      "flankAngleDegrees": 60,
      "threadForms": "UN, UNC, UNF, ISO metric",
      "pitchDiameterShiftPerSide": 4,
      "oneSided": 2
    },
    {
      "flankAngleDegrees": 55,
      "threadForms": "Whitworth, BSP, BSPT",
      "pitchDiameterShiftPerSide": 4.436,
      "oneSided": 2.218
    },
    {
      "flankAngleDegrees": 30,
      "threadForms": "Trapezoidal, Tr",
      "pitchDiameterShiftPerSide": 8.619,
      "oneSided": 4.309
    },
    {
      "flankAngleDegrees": 29,
      "threadForms": "ACME, Stub ACME",
      "pitchDiameterShiftPerSide": 8.93,
      "oneSided": 4.465
    }
  ]
}