45/64" drill size

    A 45/64" fractional drill is 0.7031 in (17.859 mm). It is the cut tap, 75% thread drill for 3/4-20.

    Decimal inch
    0.7031
    Millimeters
    17.859
    Nearest 1/64
    45/64" (+0.0000)
    Type
    fractional drill

    Nearest equivalents in other systems

    Drills closest to 45/64"
    SystemDrillInchmmDifference
    Number / letterLetter Z0.413010.490-0.2901 in
    Metric17.75 mm0.698817.750-0.0043 in

    Speeds and feeds: in mild steel an HSS drill starts at about 490 RPM and 0.0113 in/rev (5.54 IPM); in 6061 aluminum about 1,360 RPM.

    45/64" drill speeds and feeds by material

    Jobber-length twist drill, D = 0.7031 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

    45/64" drilling speeds
    MaterialHSS SFMHSS RPMCarbide SFMCarbide RPMFeed (in/rev)HSS IPMCarbide IPM
    Aluminum (6061)2501,3606003,2600.010814.735.2
    Brass / free-machining1508104002,1700.00897.2119.3
    Low-carbon steel (1018)904903001,6300.01135.5418.4
    Alloy steel (4140, annealed)703802501,3600.01194.5216.2
    Stainless 304402201508100.00932.057.53
    Gray cast iron804302501,3600.00974.1713.2
    Titanium 6Al-4V251401005400.00540.762.92
    Plastics (acetal)3001,6305002,7200.006811.118.5

    Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 490 RPM × 0.287 mm/rev = 141 mm/min.

    Worked example: 45/64" drill in 1018 steel

    1. HSS drill in low-carbon steel: 90 SFM.
    2. RPM = 3.82 × 90 ÷ 0.7031 ≈ 490 RPM.
    3. Feed for a 0.703 in drill in mild steel ≈ 0.0113 in/rev.
    4. IPM = 490 × 0.0113 = 5.54 IPM.

    Peck cycle by hole depth

    45/64" drill: depth and canned cycle
    DepthCyclePeckNote
    3×D = 2.109 in (53.6 mm)G81 (no peck)NoneUp to 3×D a sharp drill clears chips on its own.
    5×D = 3.516 in (89.3 mm)G73 chip-break1 × DChip-break pecks; full retract if chips pack (soft aluminum, stainless).
    8×D = 5.625 in (142.9 mm)G83 full retract0.5-1 × D, shrinking with depthRetract to clear chips; reduce feed ~10-20% past 5×D.

    Taps that use a 45/64" drill

    Nearest drills

    • 17.75 mm: 0.6988 in / 17.750 mm (-0.0043 in)
    • 18.0 mm: 0.7087 in / 18.000 mm (+0.0055 in)
    • 17.5 mm: 0.6890 in / 17.500 mm (-0.0141 in)
    • 18.25 mm: 0.7185 in / 18.250 mm (+0.0154 in)
    Drill speed calculator, prefilled for 45/64"Drill finder: sizes near 45/64"Fractional drill chartDecimal equivalent chart

    Common questions

    What is a 45/64" drill in decimal and mm?
    0.7031 in, or 17.859 mm; nearest number / letter drill: Letter Z (0.4130 in, -0.2901 in); nearest metric drill: 17.75 mm (0.6988 in, -0.0043 in).
    What RPM for a 45/64" drill in steel?
    In low-carbon steel (1018) an HSS 45/64" drill (0.7031 in) runs about 490 RPM at 90 SFM; a carbide drill about 1,630 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
    What feed for a 45/64" drill?
    About 0.0113 in/rev in mild steel, 0.0108 in/rev in aluminum and 0.0093 in/rev in 304 stainless. At 490 RPM that is 5.54 IPM in steel (IPM = RPM × IPR).
    What RPM for a 45/64" drill in aluminum?
    1,360 RPM with HSS (250 SFM) or up to 3,260 RPM with carbide (600 SFM), feeding about 0.0108 in/rev.
    What tap uses a 45/64" drill?
    3/4-20 (cut tap, 75% thread); 3/4-10 (form (roll) tap, 65% thread); 3/4-16 (cut tap, 50% thread).

    Nearby drill sizes

    Sources

    Material feed multipliers (aluminum 1.3×, brass 1.1×, 4140 0.85×, stainless and titanium 0.7× the mild-steel feed) are JobLine estimates. Peck guidance is JobLine shop practice. Use your drill maker's data first.

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