{
    "slug": "relief-undercut-chamfer",
    "title": "Relief Grooves & Chamfer Standards: DIN 509, GB/T 3",
    "description": "DIN 509 relief groove forms E/F/G/H with dimensions and tolerances, GB/T 3 and DIN 76 thread undercuts, and chamfer sizes with the C-notation drawing rules.",
    "lang": "en",
    "tables": [
        {
            "caption": "DIN 509 relief grooves — forms E, F, G and H (mm)",
            "columns": [
                "Form",
                "r",
                "t1",
                "t2",
                "f",
                "g",
                "Workpiece diameter d1 (mm)",
                "Duty"
            ],
            "rows": [
                {
                    "Form": "E",
                    "r": "0.2",
                    "t1": "0.1",
                    "t2": "—",
                    "f": "1",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "1.6 to 3",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "0.4",
                    "t1": "0.2",
                    "t2": "—",
                    "f": "2",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "3 to 18",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "0.6",
                    "t1": "0.2",
                    "t2": "—",
                    "f": "2",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "10 to 18",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "0.6",
                    "t1": "0.3",
                    "t2": "—",
                    "f": "2.5",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "18 to 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "0.8",
                    "t1": "0.3",
                    "t2": "—",
                    "f": "2.5",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "18 to 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "1.0",
                    "t1": "0.2",
                    "t2": "—",
                    "f": "2.5",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "18 to 50",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "E",
                    "r": "1.0",
                    "t1": "0.4",
                    "t2": "—",
                    "f": "4",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "over 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "1.2",
                    "t1": "0.2",
                    "t2": "—",
                    "f": "2.5",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "18 to 50",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "E",
                    "r": "1.2",
                    "t1": "0.4",
                    "t2": "—",
                    "f": "4",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "over 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "E",
                    "r": "1.6",
                    "t1": "0.3",
                    "t2": "—",
                    "f": "4",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "50 to 80",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "E",
                    "r": "2.5",
                    "t1": "0.4",
                    "t2": "—",
                    "f": "5",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "80 to 125",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "E",
                    "r": "4.0",
                    "t1": "0.5",
                    "t2": "—",
                    "f": "7",
                    "g": "—",
                    "Workpiece diameter d1 (mm)": "over 125",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "F",
                    "r": "0.2",
                    "t1": "0.1",
                    "t2": "0.1",
                    "f": "1",
                    "g": "0.9",
                    "Workpiece diameter d1 (mm)": "1.6 to 3",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "0.4",
                    "t1": "0.2",
                    "t2": "0.1",
                    "f": "2",
                    "g": "1.1",
                    "Workpiece diameter d1 (mm)": "3 to 18",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "0.6",
                    "t1": "0.2",
                    "t2": "0.1",
                    "f": "2",
                    "g": "1.4",
                    "Workpiece diameter d1 (mm)": "10 to 18",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "0.6",
                    "t1": "0.3",
                    "t2": "0.2",
                    "f": "2.5",
                    "g": "2.1",
                    "Workpiece diameter d1 (mm)": "18 to 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "0.8",
                    "t1": "0.3",
                    "t2": "0.2",
                    "f": "2.5",
                    "g": "2.3",
                    "Workpiece diameter d1 (mm)": "18 to 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "1.0",
                    "t1": "0.2",
                    "t2": "0.1",
                    "f": "2.5",
                    "g": "1.8",
                    "Workpiece diameter d1 (mm)": "18 to 50",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "F",
                    "r": "1.0",
                    "t1": "0.4",
                    "t2": "0.3",
                    "f": "4",
                    "g": "3.2",
                    "Workpiece diameter d1 (mm)": "over 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "1.2",
                    "t1": "0.2",
                    "t2": "0.1",
                    "f": "2.5",
                    "g": "2.0",
                    "Workpiece diameter d1 (mm)": "18 to 50",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "F",
                    "r": "1.2",
                    "t1": "0.4",
                    "t2": "0.3",
                    "f": "4",
                    "g": "3.4",
                    "Workpiece diameter d1 (mm)": "over 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "F",
                    "r": "1.6",
                    "t1": "0.3",
                    "t2": "0.2",
                    "f": "4",
                    "g": "3.1",
                    "Workpiece diameter d1 (mm)": "50 to 80",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "F",
                    "r": "2.5",
                    "t1": "0.4",
                    "t2": "0.3",
                    "f": "5",
                    "g": "4.8",
                    "Workpiece diameter d1 (mm)": "80 to 125",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "F",
                    "r": "4.0",
                    "t1": "0.5",
                    "t2": "0.3",
                    "f": "7",
                    "g": "6.4",
                    "Workpiece diameter d1 (mm)": "over 125",
                    "Duty": "Higher alternating"
                },
                {
                    "Form": "G",
                    "r": "0.4",
                    "t1": "0.2",
                    "t2": "0.2",
                    "f": "0.9",
                    "g": "1.1",
                    "Workpiece diameter d1 (mm)": "3 to 18",
                    "Duty": "Low fatigue loads only"
                },
                {
                    "Form": "H",
                    "r": "0.8",
                    "t1": "0.3",
                    "t2": "0.05",
                    "f": "2.0",
                    "g": "1.1",
                    "Workpiece diameter d1 (mm)": "18 to 80",
                    "Duty": "Normal"
                },
                {
                    "Form": "H",
                    "r": "1.2",
                    "t1": "0.3",
                    "t2": "0.05",
                    "f": "2.4",
                    "g": "1.5",
                    "Workpiece diameter d1 (mm)": "18 to 50",
                    "Duty": "Normal"
                }
            ]
        },
        {
            "caption": "Thread Undercut, External — GB/T 3-1997",
            "columns": [
                "Pitch P (mm)",
                "g2 max",
                "g1 min",
                "d8",
                "r"
            ],
            "rows": [
                {
                    "Pitch P (mm)": "0.5",
                    "g2 max": "1.5",
                    "g1 min": "0.8",
                    "d8": "d − 0.8",
                    "r": "0.2"
                },
                {
                    "Pitch P (mm)": "0.7",
                    "g2 max": "2.1",
                    "g1 min": "1.1",
                    "d8": "d − 1.1",
                    "r": "0.4"
                },
                {
                    "Pitch P (mm)": "0.8",
                    "g2 max": "2.4",
                    "g1 min": "1.3",
                    "d8": "d − 1.3",
                    "r": "0.4"
                },
                {
                    "Pitch P (mm)": "1.0",
                    "g2 max": "3.0",
                    "g1 min": "1.6",
                    "d8": "d − 1.6",
                    "r": "0.6"
                },
                {
                    "Pitch P (mm)": "1.25",
                    "g2 max": "3.75",
                    "g1 min": "2.0",
                    "d8": "d − 2.0",
                    "r": "0.6"
                },
                {
                    "Pitch P (mm)": "1.5",
                    "g2 max": "4.5",
                    "g1 min": "2.5",
                    "d8": "d − 2.3",
                    "r": "0.8"
                },
                {
                    "Pitch P (mm)": "1.75",
                    "g2 max": "5.25",
                    "g1 min": "3.0",
                    "d8": "d − 2.6",
                    "r": "1.0"
                },
                {
                    "Pitch P (mm)": "2.0",
                    "g2 max": "6.0",
                    "g1 min": "3.4",
                    "d8": "d − 3.0",
                    "r": "1.0"
                },
                {
                    "Pitch P (mm)": "2.5",
                    "g2 max": "7.5",
                    "g1 min": "4.4",
                    "d8": "d − 3.6",
                    "r": "1.2"
                },
                {
                    "Pitch P (mm)": "3.0",
                    "g2 max": "9.0",
                    "g1 min": "5.2",
                    "d8": "d − 4.4",
                    "r": "1.6"
                }
            ]
        },
        {
            "caption": "Thread Undercut, Internal — GB/T 3-1997",
            "columns": [
                "Pitch P (mm)",
                "G1 normal",
                "G1 short",
                "D5",
                "R"
            ],
            "rows": [
                {
                    "Pitch P (mm)": "0.5",
                    "G1 normal": "2",
                    "G1 short": "1",
                    "D5": "D + 0.3",
                    "R": "0.2"
                },
                {
                    "Pitch P (mm)": "0.7",
                    "G1 normal": "2.8",
                    "G1 short": "1.4",
                    "D5": "D + 0.4",
                    "R": "0.4"
                },
                {
                    "Pitch P (mm)": "0.8",
                    "G1 normal": "3.2",
                    "G1 short": "1.6",
                    "D5": "D + 0.4",
                    "R": "0.4"
                },
                {
                    "Pitch P (mm)": "1.0",
                    "G1 normal": "4",
                    "G1 short": "2",
                    "D5": "D + 0.5",
                    "R": "0.5"
                },
                {
                    "Pitch P (mm)": "1.25",
                    "G1 normal": "5",
                    "G1 short": "2.5",
                    "D5": "D + 0.6",
                    "R": "0.6"
                },
                {
                    "Pitch P (mm)": "1.5",
                    "G1 normal": "6",
                    "G1 short": "3",
                    "D5": "D + 0.8",
                    "R": "0.8"
                },
                {
                    "Pitch P (mm)": "1.75",
                    "G1 normal": "7",
                    "G1 short": "3.5",
                    "D5": "D + 0.9",
                    "R": "0.9"
                },
                {
                    "Pitch P (mm)": "2.0",
                    "G1 normal": "8",
                    "G1 short": "4",
                    "D5": "D + 1.0",
                    "R": "1.0"
                },
                {
                    "Pitch P (mm)": "2.5",
                    "G1 normal": "10",
                    "G1 short": "5",
                    "D5": "D + 1.2",
                    "R": "1.2"
                },
                {
                    "Pitch P (mm)": "3.0",
                    "G1 normal": "12",
                    "G1 short": "6",
                    "D5": "D + 1.5",
                    "R": "1.5"
                }
            ]
        },
        {
            "caption": "Thread Undercut — DIN 76-1 (European drawings)",
            "columns": [
                "Thread",
                "P",
                "dg external (h13)",
                "r",
                "dG internal (H13)",
                "g, form A",
                "g, form B",
                "g, form C",
                "g, form D"
            ],
            "rows": [
                {
                    "Thread": "M3",
                    "P": "0.5",
                    "dg external (h13)": "2.2",
                    "r": "0.2",
                    "dG internal (H13)": "3.3",
                    "g, form A": "1.75",
                    "g, form B": "1.25",
                    "g, form C": "2.7",
                    "g, form D": "2.0"
                },
                {
                    "Thread": "M4",
                    "P": "0.7",
                    "dg external (h13)": "2.9",
                    "r": "0.4",
                    "dG internal (H13)": "4.3",
                    "g, form A": "2.45",
                    "g, form B": "1.75",
                    "g, form C": "3.8",
                    "g, form D": "2.75"
                },
                {
                    "Thread": "M5",
                    "P": "0.8",
                    "dg external (h13)": "3.7",
                    "r": "0.4",
                    "dG internal (H13)": "5.3",
                    "g, form A": "2.8",
                    "g, form B": "2.0",
                    "g, form C": "4.2",
                    "g, form D": "3.0"
                },
                {
                    "Thread": "M6",
                    "P": "1.0",
                    "dg external (h13)": "4.4",
                    "r": "0.6",
                    "dG internal (H13)": "6.5",
                    "g, form A": "3.5",
                    "g, form B": "2.5",
                    "g, form C": "5.2",
                    "g, form D": "3.7"
                },
                {
                    "Thread": "M8",
                    "P": "1.25",
                    "dg external (h13)": "6.0",
                    "r": "0.6",
                    "dG internal (H13)": "8.5",
                    "g, form A": "4.4",
                    "g, form B": "3.2",
                    "g, form C": "6.7",
                    "g, form D": "4.9"
                },
                {
                    "Thread": "M10",
                    "P": "1.5",
                    "dg external (h13)": "7.7",
                    "r": "0.8",
                    "dG internal (H13)": "10.5",
                    "g, form A": "5.2",
                    "g, form B": "3.8",
                    "g, form C": "7.8",
                    "g, form D": "5.6"
                },
                {
                    "Thread": "M12",
                    "P": "1.75",
                    "dg external (h13)": "9.4",
                    "r": "1.0",
                    "dG internal (H13)": "12.5",
                    "g, form A": "6.1",
                    "g, form B": "4.3",
                    "g, form C": "9.1",
                    "g, form D": "6.1"
                },
                {
                    "Thread": "M14",
                    "P": "2.0",
                    "dg external (h13)": "11.0",
                    "r": "1.0",
                    "dG internal (H13)": "14.5",
                    "g, form A": "7.0",
                    "g, form B": "5.0",
                    "g, form C": "10.3",
                    "g, form D": "7.3"
                },
                {
                    "Thread": "M16",
                    "P": "2.0",
                    "dg external (h13)": "14.4",
                    "r": "1.2",
                    "dG internal (H13)": "18.5",
                    "g, form A": "8.7",
                    "g, form B": "6.3",
                    "g, form C": "13.0",
                    "g, form D": "9.3"
                }
            ]
        },
        {
            "caption": "Chamfer Sizes and Drawing Indication",
            "columns": [
                "Scenario",
                "Common chamfers",
                "Drawing indication",
                "Tolerance convention"
            ],
            "rows": [
                {
                    "Scenario": "External diameter",
                    "Common chamfers": "C0.5, C1, C1.5, C2",
                    "Drawing indication": "45° written as C1 or 1×45°; non-45° chamfers show angle and length separately.",
                    "Tolerance convention": "ISO 2768-m broken edges: 0.5–3 ±0.2; 3–6 ±0.5; over 6 ±1.0"
                },
                {
                    "Scenario": "Internal bore",
                    "Common chamfers": "C0.5, C1, C2",
                    "Drawing indication": "On the entry edge; the same C rules apply as outside.",
                    "Tolerance convention": "ISO 2768-1 broken-edge rows, same as external"
                },
                {
                    "Scenario": "End face",
                    "Common chamfers": "C1, C2, C3",
                    "Drawing indication": "Equal-leg C notation only at 45°.",
                    "Tolerance convention": "Per the ISO 2768 class stated in the title block"
                },
                {
                    "Scenario": "Thread end, external",
                    "Common chamfers": "See the thread chamfer table below",
                    "Drawing indication": "45° typical, 30°/60° allowed; depth at least the thread profile height.",
                    "Tolerance convention": "Transition angle α ≥ 30° (GB/T 3-1997 clause 2.3)"
                },
                {
                    "Scenario": "Thread entry, internal",
                    "Common chamfers": "See the thread chamfer table below",
                    "Drawing indication": "120° included angle typical, 90° allowed; diameter (1.0–1.05) × D.",
                    "Tolerance convention": "Countersink, not a linear C dimension (GB/T 3-1997 clause 3.3)"
                }
            ]
        },
        {
            "caption": "Thread-End Chamfers M3–M24",
            "columns": [
                "Thread",
                "P",
                "External angle",
                "Tip dia, derived (d − 1.08P)",
                "Shop rule (d − P)",
                "Internal countersink",
                "Internal dia",
                "Purpose"
            ],
            "rows": [
                {
                    "Thread": "M3",
                    "P": "0.5",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "2.46 ≈ 2.5",
                    "Shop rule (d − P)": "2.5",
                    "Internal countersink": "120°",
                    "Internal dia": "3.0–3.15",
                    "Purpose": "Guides the die or tap; protects the first thread."
                },
                {
                    "Thread": "M4",
                    "P": "0.7",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "3.24 ≈ 3.2",
                    "Shop rule (d − P)": "3.3",
                    "Internal countersink": "120°",
                    "Internal dia": "4.0–4.2",
                    "Purpose": "Eases assembly start."
                },
                {
                    "Thread": "M5",
                    "P": "0.8",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "4.14 ≈ 4.1",
                    "Shop rule (d − P)": "4.2",
                    "Internal countersink": "120°",
                    "Internal dia": "5.0–5.25",
                    "Purpose": "Removes the first-crest burr."
                },
                {
                    "Thread": "M6",
                    "P": "1.0",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "4.92 ≈ 4.9",
                    "Shop rule (d − P)": "5.0",
                    "Internal countersink": "120°",
                    "Internal dia": "6.0–6.3",
                    "Purpose": "Nut and bolt engagement lead-in."
                },
                {
                    "Thread": "M8",
                    "P": "1.25",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "6.65 ≈ 6.6",
                    "Shop rule (d − P)": "6.75",
                    "Internal countersink": "120°",
                    "Internal dia": "8.0–8.4",
                    "Purpose": "Protects the load-bearing first turns."
                },
                {
                    "Thread": "M10",
                    "P": "1.5",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "8.38 ≈ 8.4",
                    "Shop rule (d − P)": "8.5",
                    "Internal countersink": "120°",
                    "Internal dia": "10.0–10.5",
                    "Purpose": "Prevents cross-threading."
                },
                {
                    "Thread": "M12",
                    "P": "1.75",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "10.11 ≈ 10.1",
                    "Shop rule (d − P)": "10.25",
                    "Internal countersink": "120°",
                    "Internal dia": "12.0–12.6",
                    "Purpose": "Assembly lead-in."
                },
                {
                    "Thread": "M14",
                    "P": "2.0",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "11.84 ≈ 11.8",
                    "Shop rule (d − P)": "12.0",
                    "Internal countersink": "120°",
                    "Internal dia": "14.0–14.7",
                    "Purpose": "Protects the first full thread."
                },
                {
                    "Thread": "M16",
                    "P": "2.0",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "13.84 ≈ 13.8",
                    "Shop rule (d − P)": "14.0",
                    "Internal countersink": "120°",
                    "Internal dia": "16.0–16.8",
                    "Purpose": "Die entry and burr control."
                },
                {
                    "Thread": "M18",
                    "P": "2.5",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "15.30",
                    "Shop rule (d − P)": "15.5",
                    "Internal countersink": "120°",
                    "Internal dia": "18.0–18.9",
                    "Purpose": "Thread-start protection."
                },
                {
                    "Thread": "M20",
                    "P": "2.5",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "17.30",
                    "Shop rule (d − P)": "17.5",
                    "Internal countersink": "120°",
                    "Internal dia": "20.0–21.0",
                    "Purpose": "Prevents galling at the start."
                },
                {
                    "Thread": "M22",
                    "P": "2.5",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "19.30",
                    "Shop rule (d − P)": "19.5",
                    "Internal countersink": "120°",
                    "Internal dia": "22.0–23.1",
                    "Purpose": "Assembly lead-in."
                },
                {
                    "Thread": "M24",
                    "P": "3.0",
                    "External angle": "45°",
                    "Tip dia, derived (d − 1.08P)": "20.76 ≈ 20.8",
                    "Shop rule (d − P)": "21.0",
                    "Internal countersink": "120°",
                    "Internal dia": "24.0–25.2",
                    "Purpose": "Protects the first load-bearing turns."
                }
            ]
        }
    ]
}