{
  "id": "unified-thread-limits",
  "source": "https://ctrlplanner.com/walkback",
  "license": "CC-BY-4.0",
  "attribution": "ctrlPlanner, https://ctrlplanner.com/walkback",
  "title": "Unified inch screw thread pitch diameter limits",
  "standard": [
    "ASME B1.1",
    "Federal Screw Thread Specification H28"
  ],
  "description": "Pitch diameter limits for common UNC and UNF sizes in classes 2A, 3A, 2B and 3B, computed from the basic thread geometry and the class tolerance formula rather than transcribed from a table.",
  "method": "pitch = 1/n. Basic pitch diameter = D - 0.649519 x pitch. Class 2A tolerance = 0.0015 x D^(1/3) + 0.0015 x sqrt(D) + 0.015 x pitch^(2/3). Allowance on external classes 2A = 0.3 x that tolerance. Class 3A = 0.75x, internal classes = 1.3x their external counterpart. Every derived figure is computed from the unrounded tolerance and rounded once to four places.",
  "notes": [
    "Pitch diameter only. Major and minor diameter limits come from a different set of formulas this engine does not carry.",
    "Classes 1A and 1B are not published: their tolerance relationship could not be verified against a printed table, and a guessed limit on a thread is scrap.",
    "An external thread hangs below basic by its allowance; an internal thread starts at basic exactly, because the allowance is applied to the external thread only."
  ],
  "classes": [
    {
      "threadClass": "2A",
      "side": "external",
      "fit": "general purpose"
    },
    {
      "threadClass": "3A",
      "side": "external",
      "fit": "close"
    },
    {
      "threadClass": "2B",
      "side": "internal",
      "fit": "general purpose"
    },
    {
      "threadClass": "3B",
      "side": "internal",
      "fit": "close"
    }
  ],
  "rows": [
    {
      "size": "#4-40 UNC",
      "series": "UNC",
      "majorDiameter": 0.112,
      "threadsPerInch": 40,
      "threadClass": "2A",
      "basicPitchDiameter": 0.0958,
      "allowance": 0.0008,
      "tolerance": 0.0025,
      "pitchDiameterMin": 0.0925,
      "pitchDiameterMax": 0.095,
      "unit": "in"
    },
    {
      "size": "#4-40 UNC",
      "series": "UNC",
      "majorDiameter": 0.112,
      "threadsPerInch": 40,
      "threadClass": "3A",
      "basicPitchDiameter": 0.0958,
      "allowance": 0,
      "tolerance": 0.0019,
      "pitchDiameterMin": 0.0939,
      "pitchDiameterMax": 0.0958,
      "unit": "in"
    },
    {
      "size": "#4-40 UNC",
      "series": "UNC",
      "majorDiameter": 0.112,
      "threadsPerInch": 40,
      "threadClass": "2B",
      "basicPitchDiameter": 0.0958,
      "allowance": 0,
      "tolerance": 0.0033,
      "pitchDiameterMin": 0.0958,
      "pitchDiameterMax": 0.0991,
      "unit": "in"
    },
    {
      "size": "#4-40 UNC",
      "series": "UNC",
      "majorDiameter": 0.112,
      "threadsPerInch": 40,
      "threadClass": "3B",
      "basicPitchDiameter": 0.0958,
      "allowance": 0,
      "tolerance": 0.0024,
      "pitchDiameterMin": 0.0958,
      "pitchDiameterMax": 0.0982,
      "unit": "in"
    },
    {
      "size": "#6-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.138,
      "threadsPerInch": 32,
      "threadClass": "2A",
      "basicPitchDiameter": 0.1177,
      "allowance": 0.0008,
      "tolerance": 0.0028,
      "pitchDiameterMin": 0.1141,
      "pitchDiameterMax": 0.1169,
      "unit": "in"
    },
    {
      "size": "#6-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.138,
      "threadsPerInch": 32,
      "threadClass": "3A",
      "basicPitchDiameter": 0.1177,
      "allowance": 0,
      "tolerance": 0.0021,
      "pitchDiameterMin": 0.1156,
      "pitchDiameterMax": 0.1177,
      "unit": "in"
    },
    {
      "size": "#6-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.138,
      "threadsPerInch": 32,
      "threadClass": "2B",
      "basicPitchDiameter": 0.1177,
      "allowance": 0,
      "tolerance": 0.0037,
      "pitchDiameterMin": 0.1177,
      "pitchDiameterMax": 0.1214,
      "unit": "in"
    },
    {
      "size": "#6-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.138,
      "threadsPerInch": 32,
      "threadClass": "3B",
      "basicPitchDiameter": 0.1177,
      "allowance": 0,
      "tolerance": 0.0028,
      "pitchDiameterMin": 0.1177,
      "pitchDiameterMax": 0.1205,
      "unit": "in"
    },
    {
      "size": "#8-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.164,
      "threadsPerInch": 32,
      "threadClass": "2A",
      "basicPitchDiameter": 0.1437,
      "allowance": 0.0009,
      "tolerance": 0.0029,
      "pitchDiameterMin": 0.1399,
      "pitchDiameterMax": 0.1428,
      "unit": "in"
    },
    {
      "size": "#8-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.164,
      "threadsPerInch": 32,
      "threadClass": "3A",
      "basicPitchDiameter": 0.1437,
      "allowance": 0,
      "tolerance": 0.0022,
      "pitchDiameterMin": 0.1415,
      "pitchDiameterMax": 0.1437,
      "unit": "in"
    },
    {
      "size": "#8-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.164,
      "threadsPerInch": 32,
      "threadClass": "2B",
      "basicPitchDiameter": 0.1437,
      "allowance": 0,
      "tolerance": 0.0038,
      "pitchDiameterMin": 0.1437,
      "pitchDiameterMax": 0.1475,
      "unit": "in"
    },
    {
      "size": "#8-32 UNC",
      "series": "UNC",
      "majorDiameter": 0.164,
      "threadsPerInch": 32,
      "threadClass": "3B",
      "basicPitchDiameter": 0.1437,
      "allowance": 0,
      "tolerance": 0.0028,
      "pitchDiameterMin": 0.1437,
      "pitchDiameterMax": 0.1465,
      "unit": "in"
    },
    {
      "size": "#10-24 UNC",
      "series": "UNC",
      "majorDiameter": 0.19,
      "threadsPerInch": 24,
      "threadClass": "2A",
      "basicPitchDiameter": 0.1629,
      "allowance": 0.001,
      "tolerance": 0.0033,
      "pitchDiameterMin": 0.1586,
      "pitchDiameterMax": 0.1619,
      "unit": "in"
    },
    {
      "size": "#10-24 UNC",
      "series": "UNC",
      "majorDiameter": 0.19,
      "threadsPerInch": 24,
      "threadClass": "3A",
      "basicPitchDiameter": 0.1629,
      "allowance": 0,
      "tolerance": 0.0025,
      "pitchDiameterMin": 0.1604,
      "pitchDiameterMax": 0.1629,
      "unit": "in"
    },
    {
      "size": "#10-24 UNC",
      "series": "UNC",
      "majorDiameter": 0.19,
      "threadsPerInch": 24,
      "threadClass": "2B",
      "basicPitchDiameter": 0.1629,
      "allowance": 0,
      "tolerance": 0.0043,
      "pitchDiameterMin": 0.1629,
      "pitchDiameterMax": 0.1672,
      "unit": "in"
    },
    {
      "size": "#10-24 UNC",
      "series": "UNC",
      "majorDiameter": 0.19,
      "threadsPerInch": 24,
      "threadClass": "3B",
      "basicPitchDiameter": 0.1629,
      "allowance": 0,
      "tolerance": 0.0032,
      "pitchDiameterMin": 0.1629,
      "pitchDiameterMax": 0.1661,
      "unit": "in"
    },
    {
      "size": "#10-32 UNF",
      "series": "UNF",
      "majorDiameter": 0.19,
      "threadsPerInch": 32,
      "threadClass": "2A",
      "basicPitchDiameter": 0.1697,
      "allowance": 0.0009,
      "tolerance": 0.003,
      "pitchDiameterMin": 0.1658,
      "pitchDiameterMax": 0.1688,
      "unit": "in"
    },
    {
      "size": "#10-32 UNF",
      "series": "UNF",
      "majorDiameter": 0.19,
      "threadsPerInch": 32,
      "threadClass": "3A",
      "basicPitchDiameter": 0.1697,
      "allowance": 0,
      "tolerance": 0.0023,
      "pitchDiameterMin": 0.1674,
      "pitchDiameterMax": 0.1697,
      "unit": "in"
    },
    {
      "size": "#10-32 UNF",
      "series": "UNF",
      "majorDiameter": 0.19,
      "threadsPerInch": 32,
      "threadClass": "2B",
      "basicPitchDiameter": 0.1697,
      "allowance": 0,
      "tolerance": 0.0039,
      "pitchDiameterMin": 0.1697,
      "pitchDiameterMax": 0.1736,
      "unit": "in"
    },
    {
      "size": "#10-32 UNF",
      "series": "UNF",
      "majorDiameter": 0.19,
      "threadsPerInch": 32,
      "threadClass": "3B",
      "basicPitchDiameter": 0.1697,
      "allowance": 0,
      "tolerance": 0.0029,
      "pitchDiameterMin": 0.1697,
      "pitchDiameterMax": 0.1726,
      "unit": "in"
    },
    {
      "size": "1/4-20 UNC",
      "series": "UNC",
      "majorDiameter": 0.25,
      "threadsPerInch": 20,
      "threadClass": "2A",
      "basicPitchDiameter": 0.2175,
      "allowance": 0.0011,
      "tolerance": 0.0037,
      "pitchDiameterMin": 0.2127,
      "pitchDiameterMax": 0.2164,
      "unit": "in"
    },
    {
      "size": "1/4-20 UNC",
      "series": "UNC",
      "majorDiameter": 0.25,
      "threadsPerInch": 20,
      "threadClass": "3A",
      "basicPitchDiameter": 0.2175,
      "allowance": 0,
      "tolerance": 0.0028,
      "pitchDiameterMin": 0.2147,
      "pitchDiameterMax": 0.2175,
      "unit": "in"
    },
    {
      "size": "1/4-20 UNC",
      "series": "UNC",
      "majorDiameter": 0.25,
      "threadsPerInch": 20,
      "threadClass": "2B",
      "basicPitchDiameter": 0.2175,
      "allowance": 0,
      "tolerance": 0.0048,
      "pitchDiameterMin": 0.2175,
      "pitchDiameterMax": 0.2223,
      "unit": "in"
    },
    {
      "size": "1/4-20 UNC",
      "series": "UNC",
      "majorDiameter": 0.25,
      "threadsPerInch": 20,
      "threadClass": "3B",
      "basicPitchDiameter": 0.2175,
      "allowance": 0,
      "tolerance": 0.0036,
      "pitchDiameterMin": 0.2175,
      "pitchDiameterMax": 0.2211,
      "unit": "in"
    },
    {
      "size": "1/4-28 UNF",
      "series": "UNF",
      "majorDiameter": 0.25,
      "threadsPerInch": 28,
      "threadClass": "2A",
      "basicPitchDiameter": 0.2268,
      "allowance": 0.001,
      "tolerance": 0.0033,
      "pitchDiameterMin": 0.2225,
      "pitchDiameterMax": 0.2258,
      "unit": "in"
    },
    {
      "size": "1/4-28 UNF",
      "series": "UNF",
      "majorDiameter": 0.25,
      "threadsPerInch": 28,
      "threadClass": "3A",
      "basicPitchDiameter": 0.2268,
      "allowance": 0,
      "tolerance": 0.0025,
      "pitchDiameterMin": 0.2243,
      "pitchDiameterMax": 0.2268,
      "unit": "in"
    },
    {
      "size": "1/4-28 UNF",
      "series": "UNF",
      "majorDiameter": 0.25,
      "threadsPerInch": 28,
      "threadClass": "2B",
      "basicPitchDiameter": 0.2268,
      "allowance": 0,
      "tolerance": 0.0043,
      "pitchDiameterMin": 0.2268,
      "pitchDiameterMax": 0.2311,
      "unit": "in"
    },
    {
      "size": "1/4-28 UNF",
      "series": "UNF",
      "majorDiameter": 0.25,
      "threadsPerInch": 28,
      "threadClass": "3B",
      "basicPitchDiameter": 0.2268,
      "allowance": 0,
      "tolerance": 0.0032,
      "pitchDiameterMin": 0.2268,
      "pitchDiameterMax": 0.23,
      "unit": "in"
    },
    {
      "size": "5/16-18 UNC",
      "series": "UNC",
      "majorDiameter": 0.3125,
      "threadsPerInch": 18,
      "threadClass": "2A",
      "basicPitchDiameter": 0.2764,
      "allowance": 0.0012,
      "tolerance": 0.004,
      "pitchDiameterMin": 0.2712,
      "pitchDiameterMax": 0.2752,
      "unit": "in"
    },
    {
      "size": "5/16-18 UNC",
      "series": "UNC",
      "majorDiameter": 0.3125,
      "threadsPerInch": 18,
      "threadClass": "3A",
      "basicPitchDiameter": 0.2764,
      "allowance": 0,
      "tolerance": 0.003,
      "pitchDiameterMin": 0.2734,
      "pitchDiameterMax": 0.2764,
      "unit": "in"
    },
    {
      "size": "5/16-18 UNC",
      "series": "UNC",
      "majorDiameter": 0.3125,
      "threadsPerInch": 18,
      "threadClass": "2B",
      "basicPitchDiameter": 0.2764,
      "allowance": 0,
      "tolerance": 0.0053,
      "pitchDiameterMin": 0.2764,
      "pitchDiameterMax": 0.2817,
      "unit": "in"
    },
    {
      "size": "5/16-18 UNC",
      "series": "UNC",
      "majorDiameter": 0.3125,
      "threadsPerInch": 18,
      "threadClass": "3B",
      "basicPitchDiameter": 0.2764,
      "allowance": 0,
      "tolerance": 0.0039,
      "pitchDiameterMin": 0.2764,
      "pitchDiameterMax": 0.2803,
      "unit": "in"
    },
    {
      "size": "5/16-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.3125,
      "threadsPerInch": 24,
      "threadClass": "2A",
      "basicPitchDiameter": 0.2854,
      "allowance": 0.0011,
      "tolerance": 0.0037,
      "pitchDiameterMin": 0.2806,
      "pitchDiameterMax": 0.2843,
      "unit": "in"
    },
    {
      "size": "5/16-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.3125,
      "threadsPerInch": 24,
      "threadClass": "3A",
      "basicPitchDiameter": 0.2854,
      "allowance": 0,
      "tolerance": 0.0027,
      "pitchDiameterMin": 0.2827,
      "pitchDiameterMax": 0.2854,
      "unit": "in"
    },
    {
      "size": "5/16-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.3125,
      "threadsPerInch": 24,
      "threadClass": "2B",
      "basicPitchDiameter": 0.2854,
      "allowance": 0,
      "tolerance": 0.0048,
      "pitchDiameterMin": 0.2854,
      "pitchDiameterMax": 0.2902,
      "unit": "in"
    },
    {
      "size": "5/16-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.3125,
      "threadsPerInch": 24,
      "threadClass": "3B",
      "basicPitchDiameter": 0.2854,
      "allowance": 0,
      "tolerance": 0.0036,
      "pitchDiameterMin": 0.2854,
      "pitchDiameterMax": 0.289,
      "unit": "in"
    },
    {
      "size": "3/8-16 UNC",
      "series": "UNC",
      "majorDiameter": 0.375,
      "threadsPerInch": 16,
      "threadClass": "2A",
      "basicPitchDiameter": 0.3344,
      "allowance": 0.0013,
      "tolerance": 0.0044,
      "pitchDiameterMin": 0.3287,
      "pitchDiameterMax": 0.3331,
      "unit": "in"
    },
    {
      "size": "3/8-16 UNC",
      "series": "UNC",
      "majorDiameter": 0.375,
      "threadsPerInch": 16,
      "threadClass": "3A",
      "basicPitchDiameter": 0.3344,
      "allowance": 0,
      "tolerance": 0.0033,
      "pitchDiameterMin": 0.3311,
      "pitchDiameterMax": 0.3344,
      "unit": "in"
    },
    {
      "size": "3/8-16 UNC",
      "series": "UNC",
      "majorDiameter": 0.375,
      "threadsPerInch": 16,
      "threadClass": "2B",
      "basicPitchDiameter": 0.3344,
      "allowance": 0,
      "tolerance": 0.0057,
      "pitchDiameterMin": 0.3344,
      "pitchDiameterMax": 0.3401,
      "unit": "in"
    },
    {
      "size": "3/8-16 UNC",
      "series": "UNC",
      "majorDiameter": 0.375,
      "threadsPerInch": 16,
      "threadClass": "3B",
      "basicPitchDiameter": 0.3344,
      "allowance": 0,
      "tolerance": 0.0043,
      "pitchDiameterMin": 0.3344,
      "pitchDiameterMax": 0.3387,
      "unit": "in"
    },
    {
      "size": "3/8-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.375,
      "threadsPerInch": 24,
      "threadClass": "2A",
      "basicPitchDiameter": 0.3479,
      "allowance": 0.0011,
      "tolerance": 0.0038,
      "pitchDiameterMin": 0.343,
      "pitchDiameterMax": 0.3468,
      "unit": "in"
    },
    {
      "size": "3/8-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.375,
      "threadsPerInch": 24,
      "threadClass": "3A",
      "basicPitchDiameter": 0.3479,
      "allowance": 0,
      "tolerance": 0.0029,
      "pitchDiameterMin": 0.345,
      "pitchDiameterMax": 0.3479,
      "unit": "in"
    },
    {
      "size": "3/8-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.375,
      "threadsPerInch": 24,
      "threadClass": "2B",
      "basicPitchDiameter": 0.3479,
      "allowance": 0,
      "tolerance": 0.0049,
      "pitchDiameterMin": 0.3479,
      "pitchDiameterMax": 0.3528,
      "unit": "in"
    },
    {
      "size": "3/8-24 UNF",
      "series": "UNF",
      "majorDiameter": 0.375,
      "threadsPerInch": 24,
      "threadClass": "3B",
      "basicPitchDiameter": 0.3479,
      "allowance": 0,
      "tolerance": 0.0037,
      "pitchDiameterMin": 0.3479,
      "pitchDiameterMax": 0.3516,
      "unit": "in"
    },
    {
      "size": "7/16-14 UNC",
      "series": "UNC",
      "majorDiameter": 0.4375,
      "threadsPerInch": 14,
      "threadClass": "2A",
      "basicPitchDiameter": 0.3911,
      "allowance": 0.0014,
      "tolerance": 0.0047,
      "pitchDiameterMin": 0.385,
      "pitchDiameterMax": 0.3897,
      "unit": "in"
    },
    {
      "size": "7/16-14 UNC",
      "series": "UNC",
      "majorDiameter": 0.4375,
      "threadsPerInch": 14,
      "threadClass": "3A",
      "basicPitchDiameter": 0.3911,
      "allowance": 0,
      "tolerance": 0.0035,
      "pitchDiameterMin": 0.3876,
      "pitchDiameterMax": 0.3911,
      "unit": "in"
    },
    {
      "size": "7/16-14 UNC",
      "series": "UNC",
      "majorDiameter": 0.4375,
      "threadsPerInch": 14,
      "threadClass": "2B",
      "basicPitchDiameter": 0.3911,
      "allowance": 0,
      "tolerance": 0.0061,
      "pitchDiameterMin": 0.3911,
      "pitchDiameterMax": 0.3972,
      "unit": "in"
    },
    {
      "size": "7/16-14 UNC",
      "series": "UNC",
      "majorDiameter": 0.4375,
      "threadsPerInch": 14,
      "threadClass": "3B",
      "basicPitchDiameter": 0.3911,
      "allowance": 0,
      "tolerance": 0.0046,
      "pitchDiameterMin": 0.3911,
      "pitchDiameterMax": 0.3957,
      "unit": "in"
    },
    {
      "size": "1/2-13 UNC",
      "series": "UNC",
      "majorDiameter": 0.5,
      "threadsPerInch": 13,
      "threadClass": "2A",
      "basicPitchDiameter": 0.45,
      "allowance": 0.0015,
      "tolerance": 0.005,
      "pitchDiameterMin": 0.4435,
      "pitchDiameterMax": 0.4485,
      "unit": "in"
    },
    {
      "size": "1/2-13 UNC",
      "series": "UNC",
      "majorDiameter": 0.5,
      "threadsPerInch": 13,
      "threadClass": "3A",
      "basicPitchDiameter": 0.45,
      "allowance": 0,
      "tolerance": 0.0037,
      "pitchDiameterMin": 0.4463,
      "pitchDiameterMax": 0.45,
      "unit": "in"
    },
    {
      "size": "1/2-13 UNC",
      "series": "UNC",
      "majorDiameter": 0.5,
      "threadsPerInch": 13,
      "threadClass": "2B",
      "basicPitchDiameter": 0.45,
      "allowance": 0,
      "tolerance": 0.0065,
      "pitchDiameterMin": 0.45,
      "pitchDiameterMax": 0.4565,
      "unit": "in"
    },
    {
      "size": "1/2-13 UNC",
      "series": "UNC",
      "majorDiameter": 0.5,
      "threadsPerInch": 13,
      "threadClass": "3B",
      "basicPitchDiameter": 0.45,
      "allowance": 0,
      "tolerance": 0.0048,
      "pitchDiameterMin": 0.45,
      "pitchDiameterMax": 0.4548,
      "unit": "in"
    },
    {
      "size": "1/2-20 UNF",
      "series": "UNF",
      "majorDiameter": 0.5,
      "threadsPerInch": 20,
      "threadClass": "2A",
      "basicPitchDiameter": 0.4675,
      "allowance": 0.0013,
      "tolerance": 0.0043,
      "pitchDiameterMin": 0.4619,
      "pitchDiameterMax": 0.4662,
      "unit": "in"
    },
    {
      "size": "1/2-20 UNF",
      "series": "UNF",
      "majorDiameter": 0.5,
      "threadsPerInch": 20,
      "threadClass": "3A",
      "basicPitchDiameter": 0.4675,
      "allowance": 0,
      "tolerance": 0.0032,
      "pitchDiameterMin": 0.4643,
      "pitchDiameterMax": 0.4675,
      "unit": "in"
    },
    {
      "size": "1/2-20 UNF",
      "series": "UNF",
      "majorDiameter": 0.5,
      "threadsPerInch": 20,
      "threadClass": "2B",
      "basicPitchDiameter": 0.4675,
      "allowance": 0,
      "tolerance": 0.0056,
      "pitchDiameterMin": 0.4675,
      "pitchDiameterMax": 0.4731,
      "unit": "in"
    },
    {
      "size": "1/2-20 UNF",
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