Drill Bit Size Chart
Number · Letter · Fractional
120+ drill sizes from #80 (0.34mm) to 1½" (38.1mm) with exact metric conversions and tap drill applications. Search by drill number, letter, or millimeter.
Drill Systems
Smallest standard number drill. Used for micro-drilling in electronics and watchmaking. Requires pin vise or precision chuck.
Very small drill. Used in PCB fabrication and precision instruments.
Fine drill for electronics and model making. Close to 1mm.
Tap drill for 0-80 UNF (0.0465"). Common in miniature instrumentation.
Tap drill for 1-64 UNC (0.052"). Small screw thread tap drill.
Tap drill for 1-72 UNF (0.055"). Fine thread small tap drill.
Tap drill for 2-56 UNC (0.0595"). Very common small screw tap drill.
Tap drill for 2-64 UNC and 3-48 UNC. Close to 1.6mm metric.
Tap drill for 3-56 UNF (0.070"). Close to 1.8mm.
Tap drill for 4-40 UNC (0.073"). Common small screw in US.
Tap drill for 4-48 UNF. Close to 2.0mm.
Close to 2.0mm. Used for clearance holes for #2 screws.
Tap drill for 5-44 UNC. Close to 2.05mm.
Tap drill for 3-48 UNC (alternate). Close to 2.1mm.
Tap drill for 5-40 UNC. Close to 2.2mm.
Tap drill for 6-40 UNC (0.089"). Common in US electronics.
Tap drill for 6-32 UNC (alternate, 0.0935"). Close to 2.4mm.
Close to 2.5mm. Used for clearance holes for #4 screws.
Tap drill for 6-32 UNC (0.098"). Very common in US hardware.
Close to 2.5mm. Tap drill for 3-48 UNC (alternate).
Tap drill for 5-44 UNC (alternate). Close to 2.6mm.
Tap drill for 6-40 UNC (alternate). Close to 2.65mm.
Tap drill for 8-32 UNC (0.1065"). Close to 2.7mm.
Tap drill for 6-40 UNF (alternate). Close to 2.8mm. Also clearance for #6 screws.
Close to 2.8mm. Used for various small tap applications.
Tap drill for 4-40 UNC (clearance). Close to 2.9mm.
Close to 3.0mm. Tap drill for 8-36 UNF.
Tap drill for 10-24 UNC (0.120"). Close to 3.0mm. Common in US hardware.
Tap drill for 10-32 UNF (0.1285"). Close to 3.3mm.
Tap drill for 8-32 UNC (alternate) and 10-24 UNC. Close to 3.5mm.
Tap drill for 10-32 UNF (alternate). Close to 3.6mm.
Tap drill for 3/16-24 UNF. Close to 3.7mm.
Tap drill for 10-32 UNF (alternate). Close to 3.75mm.
Tap drill for 10-24 UNC (alternate). Close to 3.8mm. Also clearance for #8 screws.
Close to 3.9mm. Used for various tap applications.
Close to 4.0mm. Tap drill for 12-24 UNC.
Close to 4.0mm. Tap drill for 10-32 UNF (alternate).
Tap drill for 10-32 UNF (0.159"). Close to 4.0mm. Very common.
Tap drill for 12-28 UNF. Close to 4.1mm.
Tap drill for 12-24 UNC (alternate). Close to 4.2mm.
Close to 4.3mm. Used for clearance holes for #10 screws.
Tap drill for 12-24 UNC. Close to 4.4mm.
Tap drill for 12-28 UNF (alternate). Close to 4.5mm.
Close to 4.6mm. Used for various tap applications.
Close to 4.6mm. Tap drill for 1/4-20 UNC (alternate).
Close to 4.7mm. Tap drill for 1/4-28 UNF.
Close to 4.8mm. Tap drill for 1/4-20 UNC.
Close to 4.9mm. Tap drill for 1/4-28 UNF (alternate).
Close to 5.0mm. Tap drill for 1/4-20 UNC (alternate).
Close to 5.0mm. Tap drill for 1/4-28 UNF (alternate).
Tap drill for 1/4-20 UNC. Close to 5.0mm. Common.
Tap drill for 1/4-28 UNF. Close to 5.1mm.
Close to 5.2mm. Clearance for #12 screws.
Close to 5.2mm. Tap drill for 5/16-18 UNC (alternate).
Close to 5.3mm. Tap drill for 5/16-24 UNF.
Tap drill for 5/16-18 UNC. Close to 5.4mm.
Close to 5.6mm. Tap drill for 5/16-24 UNF (alternate).
Largest number drill. Tap drill for 5/16-18 UNC (alternate). Close to 5.8mm.
Tap drill for 5/16-18 UNC (alternate). Close to 6.0mm.
Close to 6.0mm. Tap drill for 5/16-24 UNF (alternate).
Close to 6.1mm. Clearance for 1/4" bolts.
Close to 6.25mm. Tap drill for 5/16-18 UNC.
Exactly 1/4 inch. Tap drill for 5/16-18 UNC (alternate). Common reference size.
Tap drill for 5/16-24 UNF. Close to 6.5mm.
Tap drill for 3/8-24 UNF. Close to 6.6mm.
Close to 6.8mm. Tap drill for 3/8-16 UNC (alternate).
Tap drill for 3/8-16 UNC. Close to 7.0mm.
Close to 7.0mm. Tap drill for 3/8-24 UNF (alternate).
Tap drill for 3/8-16 UNC (alternate). Close to 7.14mm. Common.
Close to 7.4mm. Clearance for 5/16" bolts.
Close to 7.5mm. Tap drill for 7/16-20 UNF.
Tap drill for 7/16-14 UNC. Close to 7.7mm.
Close to 8.0mm. Clearance for 3/8" bolts.
Tap drill for 7/16-14 UNC (alternate). Close to 8.2mm.
Tap drill for 1/2-13 UNC. Close to 8.5mm. Very common.
Close to 8.6mm. Tap drill for 1/2-20 UNF.
Close to 8.8mm. Tap drill for 1/2-13 UNC (alternate).
Close to 9.1mm. Tap drill for 1/2-20 UNF (alternate).
Tap drill for 9/16-12 UNC. Close to 9.35mm.
Close to 9.6mm. Tap drill for 9/16-18 UNF.
Close to 9.8mm. Tap drill for 5/8-11 UNC.
Tap drill for 5/8-11 UNC (alternate). Close to 10.1mm.
Close to 10.3mm. Tap drill for 5/8-18 UNF.
Largest letter drill. Close to 10.5mm. Clearance for 1/2" bolts.
Smallest standard fractional drill. Tap drill for #2 and #3 screws. Close to 1.6mm.
Close to 2.0mm. Tap drill for #4 screws.
Tap drill for #6 screws. Close to 2.4mm.
Tap drill for #8 screws. Close to 2.8mm.
Very common size. Close to 3.2mm. Clearance for #5 and #6 screws.
Close to 3.6mm. Tap drill for #10 screws.
Close to 4.0mm. Clearance for #8 screws.
Close to 4.4mm. Tap drill for #12 screws.
Common size. Close to 4.8mm. Clearance for #10 screws.
Close to 5.2mm. Tap drill for 1/4" screws.
Close to 5.6mm. Clearance for #12 screws.
Close to 6.0mm. Clearance for 1/4" screws.
Very common. Exactly 6.35mm. Clearance for 1/4" bolts (close fit).
Close to 6.75mm. Tap drill for 5/16" screws.
Close to 7.14mm. Tap drill for 3/8" screws.
Close to 7.5mm. Clearance for 5/16" bolts.
Common. Close to 8.0mm. Clearance for 5/16" bolts (close fit).
Close to 8.3mm. Tap drill for 3/8" screws.
Close to 8.7mm. Clearance for 3/8" bolts.
Close to 9.1mm. Tap drill for 7/16" screws.
Very common. Close to 9.5mm. Clearance for 3/8" bolts (close fit).
Close to 9.9mm. Tap drill for 1/2" screws.
Close to 10.3mm. Clearance for 7/16" bolts.
Close to 10.7mm. Tap drill for 9/16" screws.
Common. Close to 11.1mm. Clearance for 7/16" bolts.
Close to 11.5mm. Tap drill for 5/8" screws.
Close to 11.9mm. Clearance for 1/2" bolts.
Very common. Exactly 12.7mm. Clearance for 1/2" bolts (close fit).
Smallest commonly available metric drill. Used in precision electronics and watchmaking.
Common small metric drill. Used in PCB work and precision instruments.
Tap drill for M1.6×0.35. Close to #53 drill.
Tap drill for M2.5×0.45. Close to #47 drill.
Tap drill for M3×0.5. Close to #39 drill. Very common.
Very common. Tap drill for M3.5×0.6. Close to #31 drill.
Tap drill for M4×0.7. Close to #30 drill.
Common. Tap drill for M4.5×0.75. Close to #22 drill.
Tap drill for M5×0.8. Close to #19 drill.
Very common. Tap drill for M6×1.0. Close to #9 drill.
Common. Clearance for M6 bolts. Close to D drill (0.246").
Tap drill for M8×1.25. Close to H drill (0.266"). Very common.
Tap drill for M8×1.0 (fine). Close to J drill.
Common. Clearance for M8 bolts. Close to O drill.
Tap drill for M10×1.5. Close to Q drill (0.332"). Very common.
Tap drill for M10×1.0 (fine). Close to T drill.
Common. Clearance for M10 bolts. Close to X drill.
Tap drill for M12×1.75. Close to Y drill.
Tap drill for M12×1.5 (fine). No close letter/number equivalent.
Common. Tap drill for M14×2.0. Clearance for M12 bolts.
Tap drill for M16×2.0. Clearance for M14 bolts.
Tap drill for M20×2.5. No close fractional equivalent.
Tap drill for M24×3.0. No close fractional equivalent.
Tap drill for M30×3.5. No close fractional equivalent.
Tap drill for #4-40 UNC thread. #43 drill = 2.261mm. 75% thread engagement. Most common small US screw thread.
Tap drill for #6-32 UNC thread. #36 drill = 2.705mm. 75% thread engagement. Very common in US hardware.
Tap drill for #8-32 UNC thread. #29 drill = 3.454mm. 75% thread engagement. Common in US electronics and hardware.
Tap drill for #10-24 UNC thread. #25 drill = 3.797mm. 75% thread engagement. Coarse thread for #10 screws.
Tap drill for #10-32 UNF thread. #21 drill = 4.039mm. 75% thread engagement. Fine thread for #10 screws.
Tap drill for 1/4-20 UNC thread. #7 drill = 5.105mm. 75% thread engagement. Very common US thread.
Tap drill for 5/16-18 UNC thread. F drill = 6.528mm. 75% thread engagement. Common structural thread.
Tap drill for 3/8-16 UNC thread. 5/16" drill = 7.938mm. 75% thread engagement. Common heavy-duty thread.
Tap drill for 1/2-13 UNC thread. 27/64" drill = 10.716mm. 75% thread engagement. Or use Q drill (0.332") for 75%.
Drill Bit Size Chart Advanced Efficiency Guide
Drill Bit Size Chart Efficiency Optimization & Best Practices
Number, letter, and fractional drill systems
US drill sizes use three systems: Number drills (#80 smallest to #1 largest, 0.0135" to 0.228"), Letter drills (A smallest to Z largest, 0.234" to 0.413"), and Fractional drills (1/16" and up in 1/64" increments). The systems overlap: #1 (0.228") flows into A (0.234"), and Z (0.413") flows into fractional sizes. Metric drills (0.5mm and up) run in parallel and often have close equivalents in the US systems.
Finding the right tap drill
For UNC/UNF threads, tap drill = major diameter − pitch (same as metric). For 75% thread engagement: 1/4-20 → 0.250 − 0.050 = 0.200" → use #7 drill (0.201"). For 50% engagement (easier tapping in hard materials), use one size larger. Always use cutting fluid when tapping steel. For blind holes, use spiral flute taps that push chips ahead.
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Engineering Methodology & Design Standards: Drill Bit Size Chart Number · Letter · Fractional
Discipline: Engineering Metrology, SI/Imperial Unit Conversion & Applied Physics
Governing Mathematical Formulation
In professional Engineering Metrology, SI/Imperial Unit Conversion & Applied Physics workflows, accurate sizing and performance verification require consistent unit normalization and adherence to closed-form analytical mechanics. This Drill Bit Size Chart Number · Letter · Fractional utility implements the standardized engineering formulation:
Standardized parametric evaluation for Drill Bit Size Chart Number · Letter · FractionalComplete drill bit size chart: number drills (#1-#80), letter drills (A-Z), and fractional inch drills with metric conversions and tap drill applications. Every input change triggers an instant client-side recalculation across all coupled dependent variables, enabling rapid sensitivity analysis during preliminary and detailed CAD design phases.
Applicable Codes, Standards & CAD Integration
Maintain full double-precision floating-point accuracy during intermediate engineering calculations and apply rounding only to final drawing callouts per ASME Y14.5 / ISO 80000 rules.
Engineering Verification Note: Analytical models assume homogeneous material behavior, steady-state boundary loading, and consistent dimensional units. Always apply appropriate service factors, corrosion allowances, or load and resistance factor design (LRFD / ASD) safety margins required by your governing code.
Frequently Asked Engineering Questions
Technical reference & verification guidelines for Drill Bit Size Chart Number · Letter · Fractional
What governing equation and methodology does the Drill Bit Size Chart Number · Letter · Fractional use?
The Drill Bit Size Chart Number · Letter · Fractional evaluates complete drill bit size chart: number drills (#1-#80), letter drills (a-z), and fractional inch drills with metric conversions and tap drill applications within the Engineering Metrology, SI/Imperial Unit Conversion & Applied Physics domain using the governing formulation: Standardized parametric evaluation for Drill Bit Size Chart Number · Letter · Fractional. All intermediate quantities are computed in double-precision floating-point arithmetic to prevent cumulative rounding drift before final design verification.
Which international engineering standards apply to Drill Bit Size Chart Number · Letter · Fractional calculations?
Calculations and boundary assumptions in this utility align with recognized industry references including NIST Special Publication 811 (Guide for the Use of the International System of Units), ISO 80000-1 (Quantities and Units), BIPM SI Brochure (9th Edition). When preparing formal calculation packages or P.E. stamp submittals, always verify local jurisdictional code amendments and project-specific safety factors.
How should I integrate results from the Drill Bit Size Chart Number · Letter · Fractional into my CAD or BIM workflow?
Maintain full double-precision floating-point accuracy during intermediate engineering calculations and apply rounding only to final drawing callouts per ASME Y14.5 / ISO 80000 rules. Using the baseline benchmark (standard nominal boundary parameters for Drill Bit Size Chart Number · Letter · Fractional), the solver yields verified design compliance metrics for Drill Bit Size Chart Number · Letter · Fractional, which can be directly cross-referenced against your parametric 3D assembly constraints, 2D fabrication drawings, or bill of materials (BOM).