#27 drill size

    A #27 number (wire-gauge) drill is 0.1440 in (3.658 mm). It is the cut tap, 50% thread drill for 8-32.

    Decimal inch
    0.1440
    Millimeters
    3.658
    Nearest 1/64
    9/64" (+0.0034)
    Type
    number (wire-gauge) drill

    Nearest equivalents in other systems

    Drills closest to #27
    SystemDrillInchmmDifference
    Fractional9/64"0.14063.572-0.0034 in
    Metric3.7 mm0.14573.700+0.0017 in

    Speeds and feeds: in mild steel an HSS drill starts at about 2,390 RPM and 0.0035 in/rev (8.37 IPM); in 6061 aluminum about 6,630 RPM.

    #27 drill speeds and feeds by material

    Jobber-length twist drill, D = 0.1440 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

    #27 drilling speeds
    MaterialHSS SFMHSS RPMCarbide SFMCarbide RPMFeed (in/rev)HSS IPMCarbide IPM
    Aluminum (6061)2506,63060015,9200.003321.952.5
    Brass / free-machining1503,98040010,6100.002811.129.7
    Low-carbon steel (1018)902,3903007,9600.00358.3727.9
    Alloy steel (4140, annealed)701,8602506,6300.00356.5123.2
    Stainless 304401,0601503,9800.00232.449.15
    Gray cast iron802,1202506,6300.00224.6614.6
    Titanium 6Al-4V256601002,6500.00181.194.77
    Plastics (acetal)3007,96050013,2600.004838.263.6

    Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 2,390 RPM × 0.089 mm/rev = 212 mm/min.

    Worked example: #27 drill in 1018 steel

    1. HSS drill in low-carbon steel: 90 SFM.
    2. RPM = 3.82 × 90 ÷ 0.1440 ≈ 2,390 RPM.
    3. Feed for a 0.144 in drill in mild steel ≈ 0.0035 in/rev.
    4. IPM = 2,390 × 0.0035 = 8.37 IPM.

    Peck cycle by hole depth

    #27 drill: depth and canned cycle
    DepthCyclePeckNote
    3×D = 0.432 in (11 mm)G81 (no peck)NoneUp to 3×D a sharp drill clears chips on its own.
    5×D = 0.720 in (18.3 mm)G73 chip-break1 × DChip-break pecks; full retract if chips pack (soft aluminum, stainless).
    8×D = 1.152 in (29.3 mm)G83 full retract0.5-1 × D, shrinking with depthRetract to clear chips; reduce feed ~10-20% past 5×D.

    Taps that use a #27 drill

    Nearest drills

    • 3.7 mm: 0.1457 in / 3.700 mm (+0.0017 in)
    • 3.6 mm: 0.1417 in / 3.600 mm (-0.0023 in)
    • #26: 0.1470 in / 3.734 mm (+0.0030 in)
    • 9/64": 0.1406 in / 3.572 mm (-0.0034 in)
    Drill speed calculator, prefilled for #27Drill finder: sizes near #27Number drill chartDecimal equivalent chart

    Common questions

    What is a #27 drill in decimal and mm?
    0.1440 in, or 3.658 mm; nearest fractional drill: 9/64" (0.1406 in, -0.0034 in); nearest metric drill: 3.7 mm (0.1457 in, +0.0017 in).
    What RPM for a #27 drill in steel?
    In low-carbon steel (1018) an HSS #27 drill (0.1440 in) runs about 2,390 RPM at 90 SFM; a carbide drill about 7,960 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
    What feed for a #27 drill?
    About 0.0035 in/rev in mild steel, 0.0033 in/rev in aluminum and 0.0023 in/rev in 304 stainless. At 2,390 RPM that is 8.37 IPM in steel (IPM = RPM × IPR).
    What RPM for a #27 drill in aluminum?
    6,630 RPM with HSS (250 SFM) or up to 15,920 RPM with carbide (600 SFM), feeding about 0.0033 in/rev.
    What tap uses a #27 drill?
    8-32 (cut tap, 50% thread); 4-48 (Helicoil / STI insert (#4-48×1D)).

    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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