Letter V drill size

    A letter V drill is 0.3770 in (9.576 mm).

    Decimal inch
    0.3770
    Millimeters
    9.576
    Nearest 1/64
    3/8" (+0.0020)
    Type
    letter drill

    Nearest equivalents in other systems

    Drills closest to Letter V
    SystemDrillInchmmDifference
    Fractional3/8"0.37509.525-0.0020 in
    Metric9.6 mm0.37809.600+0.0009 in

    Speeds and feeds: in mild steel an HSS drill starts at about 910 RPM and 0.0095 in/rev (8.65 IPM); in 6061 aluminum about 2,530 RPM.

    Letter V drill speeds and feeds by material

    Jobber-length twist drill, D = 0.3770 in. RPM = 3.82 × SFM ÷ D, rounded to 10. Feed per rev scales with diameter and material; IPM = RPM × IPR.

    Letter V drilling speeds
    MaterialHSS SFMHSS RPMCarbide SFMCarbide RPMFeed (in/rev)HSS IPMCarbide IPM
    Aluminum (6061)2502,5306006,0800.008521.551.7
    Brass / free-machining1501,5204004,0500.00639.5825.5
    Low-carbon steel (1018)909103003,0400.00958.6528.9
    Alloy steel (4140, annealed)707102502,5300.01057.4626.6
    Stainless 304404101501,5200.00632.589.58
    Gray cast iron808102502,5300.00655.2716.4
    Titanium 6Al-4V252501001,0100.00431.084.34
    Plastics (acetal)3003,0405005,0700.005015.225.4

    Metric: Vc (m/min) = SFM × 0.3048; feed (mm/rev) = in/rev × 25.4. In steel, 910 RPM × 0.241 mm/rev = 220 mm/min.

    Worked example: letter V drill in 1018 steel

    1. HSS drill in low-carbon steel: 90 SFM.
    2. RPM = 3.82 × 90 ÷ 0.3770 ≈ 910 RPM.
    3. Feed for a 0.377 in drill in mild steel ≈ 0.0095 in/rev.
    4. IPM = 910 × 0.0095 = 8.65 IPM.

    Peck cycle by hole depth

    Letter V drill: depth and canned cycle
    DepthCyclePeckNote
    3×D = 1.131 in (28.7 mm)G81 (no peck)NoneUp to 3×D a sharp drill clears chips on its own.
    5×D = 1.885 in (47.9 mm)G73 chip-break1 × DChip-break pecks; full retract if chips pack (soft aluminum, stainless).
    8×D = 3.016 in (76.6 mm)G83 full retract0.5-1 × D, shrinking with depthRetract to clear chips; reduce feed ~10-20% past 5×D.

    Taps that use a letter V drill

    No standard UNC, UNF or metric tap in our tables calls for a letter V drill. Use it for clearance, pilot or reamer prep holes.

    Nearest drills

    • 9.6 mm: 0.3780 in / 9.600 mm (+0.0009 in)
    • 3/8": 0.3750 in / 9.525 mm (-0.0020 in)
    • 9.5 mm: 0.3740 in / 9.500 mm (-0.0030 in)
    • 9.7 mm: 0.3819 in / 9.700 mm (+0.0049 in)
    Drill speed calculator, prefilled for letter VDrill finder: sizes near letter VLetter drill chartDecimal equivalent chart

    Common questions

    What is a letter V drill in decimal and mm?
    0.3770 in, or 9.576 mm; nearest fractional drill: 3/8" (0.3750 in, -0.0020 in); nearest metric drill: 9.6 mm (0.3780 in, +0.0009 in).
    What RPM for a letter V drill in steel?
    In low-carbon steel (1018) an HSS letter V drill (0.3770 in) runs about 910 RPM at 90 SFM; a carbide drill about 3,040 RPM at 300 SFM. RPM = 3.82 × SFM ÷ D.
    What feed for a letter V drill?
    About 0.0095 in/rev in mild steel, 0.0085 in/rev in aluminum and 0.0063 in/rev in 304 stainless. At 910 RPM that is 8.65 IPM in steel (IPM = RPM × IPR).
    What RPM for a letter V drill in aluminum?
    2,530 RPM with HSS (250 SFM) or up to 6,080 RPM with carbide (600 SFM), feeding about 0.0085 in/rev.
    What size is a letter V drill?
    0.3770 in / 9.576 mm. The nearest other drills are 9.6 mm (0.3780 in), 3/8" (0.3750 in), 9.5 mm (0.3740 in).

    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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