UNC / UNF Thread
Reference Table
#0 through 1-1/2" — coarse (UNC) and fine (UNF) threads with TPI, tap drill sizes, clearance holes, and thread engagement data.
Thread Series
Smallest UNC thread. Used in miniature instruments, electronics, and watchmaking. Tap drill #56 = 1.181mm. Very delicate — use care when tapping.
Small UNC thread. Used in precision instruments and small assemblies. Tap drill #53 = 1.511mm.
Very common small thread in US. Used in electronics, model making, and small hardware. Tap drill #50 = 1.778mm.
Small UNC thread. Less common than #2-56 or #4-40. Tap drill #47 = 1.994mm.
Most common small US thread. Used everywhere in electronics, consumer products, and small hardware. Tap drill #43 = 2.261mm.
Less common size. Used in specialized hardware. Tap drill #38 = 2.578mm. Close to 1/8" diameter.
Extremely common in US. Used in electrical boxes, computers, and general hardware. Tap drill #36 = 2.705mm. Sheet metal screw equivalent available.
Very common medium-small thread. Used in electronics, machinery, and consumer products. Tap drill #29 = 3.454mm.
Common medium thread. Used in general hardware, brackets, and machinery. Tap drill #25 = 3.797mm. Coarse version of #10.
Less common size between #10 and 1/4. Used in specialized hardware. Tap drill #16 = 4.496mm.
One of the most common US threads. Used in machinery, automotive, and construction. Tap drill #7 = 5.105mm. Close to M6 in size.
Common structural thread. Used in machinery, automotive, and structural connections. Tap drill F = 6.528mm. Close to M8 in size.
Very common heavy-duty thread. Used in machinery, automotive, and construction. Tap drill 5/16" = 7.938mm. Close to M10 in size.
Heavy machinery thread. Tap drill U = 9.347mm. Used in automotive and heavy equipment.
Major structural thread. Used in construction, machinery, and heavy equipment. Tap drill 27/64" = 10.716mm. Close to M12 in size.
Heavy structural thread. Less common than 1/2-13. Tap drill 31/64" = 12.303mm.
Heavy-duty structural thread. Used in construction and heavy machinery. Tap drill 17/32" = 13.494mm. Close to M16 in size.
Major structural thread. Used in heavy construction, machinery, and pressure vessels. Tap drill 21/32" = 16.669mm.
Very heavy structural thread. Tap drill 49/64" = 19.447mm. Used in heavy machinery and structural connections.
Large structural thread. Tap drill 7/8" = 22.225mm. Used in heavy construction and large machinery.
Very large thread. Tap drill 63/64" = 25.003mm. Used in heavy structural and industrial applications.
Large structural thread. Tap drill 1-7/64" = 28.179mm. Used in heavy construction and large equipment.
Largest commonly used UNC thread. Tap drill 1-11/32" = 34.131mm. Used in heavy structural connections.
Same as UNC for #0 — only one thread series at this size. 80 TPI is the standard for #0.
Fine thread version of #1. More TPI than #1-64. Used where finer adjustment or better locking needed. Tap drill #53.
Fine thread version of #2. 64 TPI vs 56 TPI (UNC). Tap drill #50 = 1.778mm.
Fine thread version of #3. 56 TPI vs 48 TPI (UNC). Tap drill #45 = 2.083mm.
Fine thread version of #4. 48 TPI vs 40 TPI (UNC). Used in precision instruments. Tap drill #42 = 2.375mm.
Fine thread version of #5. 44 TPI vs 40 TPI (UNC). Tap drill #37 = 2.642mm.
Fine thread version of #6. 40 TPI vs 32 TPI (UNC). Used where vibration resistance matters. Tap drill #33 = 2.870mm.
Fine thread version of #8. 36 TPI vs 32 TPI (UNC). Used in precision assemblies. Tap drill #29 = 3.454mm.
Very common fine thread. Used in electronics, machinery, and precision hardware. 32 TPI vs 24 TPI (UNC). Tap drill #21 = 4.039mm.
Fine thread version of #12. 28 TPI vs 24 TPI (UNC). Less common. Tap drill #16 = 4.496mm.
Common fine thread. Used in hydraulic fittings, precision instruments, and automotive. 28 TPI vs 20 TPI (UNC). Tap drill #3 = 5.410mm.
Fine thread for 5/16". Used in hydraulic fittings and precision assemblies. 24 TPI vs 18 TPI (UNC). Tap drill I = 6.909mm.
Common fine thread. Used in hydraulic fittings, automotive, and precision machinery. 24 TPI vs 16 TPI (UNC). Tap drill Q = 8.433mm.
Fine thread for 7/16". 20 TPI vs 14 TPI (UNC). Tap drill 25/64" = 9.922mm. Used in automotive and hydraulic applications.
Fine thread for 1/2". Very common in hydraulic fittings (JIC). 20 TPI vs 13 TPI (UNC). Tap drill 29/64" = 11.509mm.
Fine thread for 9/16". 18 TPI vs 12 TPI (UNC). Tap drill 33/64" = 13.097mm. Used in heavy hydraulic systems.
Fine thread for 5/8". Common in hydraulic fittings. 18 TPI vs 11 TPI (UNC). Tap drill 37/64" = 14.684mm.
Fine thread for 3/4". Used in hydraulic and high-pressure applications. 16 TPI vs 10 TPI (UNC). Tap drill 11/16" = 17.463mm.
Fine thread for 7/8". 14 TPI vs 9 TPI (UNC). Tap drill 49/64" = 19.447mm. Used in heavy machinery.
Fine thread for 1". 12 TPI vs 8 TPI (UNC). Tap drill 59/64" = 23.416mm. Used in precision heavy machinery.
Fine thread for 1-1/8". 12 TPI vs 7 TPI (UNC). Tap drill 1-3/64" = 26.591mm.
Fine thread for 1-1/4". 12 TPI vs 7 TPI (UNC). Tap drill 1-11/64" = 29.769mm.
Fine thread for 1-1/2". 12 TPI vs 6 TPI (UNC). Tap drill 1-23/64" = 34.528mm. Used in large precision assemblies.
Close fit clearance for #4 screw. 1/8" = 3.175mm. Used where precise alignment is required.
Normal fit clearance for #4 screw. 9/64" = 3.572mm. Standard clearance for general use.
Close fit clearance for #6 screw. 9/64" = 3.572mm.
Normal fit clearance for #6 screw. 5/32" = 3.969mm.
Close fit clearance for #8 screw. 5/32" = 3.969mm.
Normal fit clearance for #8 screw. 3/16" = 4.763mm.
Close fit clearance for #10 screw. 3/16" = 4.763mm.
Normal fit clearance for #10 screw. 7/32" = 5.556mm.
Close fit clearance for 1/4" bolt. Exact size — requires precise drilling. 6.350mm.
Normal fit clearance for 1/4" bolt. 9/32" = 7.144mm.
Close fit clearance for 5/16" bolt. Exact size. 7.938mm.
Normal fit clearance for 5/16" bolt. 11/32" = 8.731mm.
Close fit clearance for 3/8" bolt. Exact size. 9.525mm.
Normal fit clearance for 3/8" bolt. 13/32" = 10.319mm.
Close fit clearance for 1/2" bolt. Exact size. 12.700mm.
Normal fit clearance for 1/2" bolt. 17/32" = 13.494mm.
Close fit clearance for 5/8" bolt. Exact size. 15.875mm.
Normal fit clearance for 5/8" bolt. 21/32" = 16.669mm.
Close fit clearance for 3/4" bolt. Exact size. 19.050mm.
Normal fit clearance for 3/4" bolt. 13/16" = 20.638mm.
Most common tolerance class for general applications. 2A = external (bolt), 2B = internal (nut). Provides reasonable fit with manufacturing economy. Default for commercial fasteners.
Tighter tolerance for precision applications. 3A = external, 3B = internal. Used in aerospace, instrumentation, and where precise fit is critical. No allowance for plating.
Wide tolerance for rough applications. 1A = external, 1B = internal. Used for quick assembly where fit is not critical. Rare in modern practice.
75% thread engagement is standard for UNC/UNF tapping. Balances strength and ease of tapping. Tap drill formula: Major Ø − (1/TPI). Example: 1/4-20 → 0.250 − 0.050 = 0.200" → #7 drill.
50% thread engagement for hard or tough materials. Easier tapping, less tap breakage. Acceptable for most non-critical applications. Use one drill size larger than 75%.
UNC/UNF Imperial Thread Advanced Efficiency Guide
UNC/UNF Imperial Thread Efficiency Optimization & Best Practices
UNC vs UNF — when to use which
UNC (coarse) is the default for general fastening — stronger threads, easier assembly, less prone to cross-threading, and better for soft or brittle materials. UNF (fine) is used for: (1) thin walls where thread depth is limited, (2) adjustment and locking applications (finer pitch = more friction), (3) vibration resistance (finer threads resist loosening), (4) hydraulic and pressure fittings (more thread engagement per unit length). Most US automotive and machinery uses UNC; aerospace uses more UNF.
Tap drill formula for imperial threads
For UNC/UNF threads, tap drill = Major Diameter − (1/TPI). Example: 1/4-20 UNC → 0.250 − (1/20) = 0.250 − 0.050 = 0.200" → use #7 drill (0.201"). For 10-32 UNF → 0.190 − (1/32) = 0.190 − 0.03125 = 0.159" → use #21 drill (0.159"). This gives approximately 75% thread engagement. For hard materials, use one size larger for easier tapping.
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Engineering Methodology & Design Standards: UNC / UNF Thread Reference Table
Discipline: Fastener Engineering & Bolted Joint Mechanics
Governing Mathematical Formulation
In professional Fastener Engineering & Bolted Joint Mechanics workflows, accurate sizing and performance verification require consistent unit normalization and adherence to closed-form analytical mechanics. This UNC / UNF Thread Reference Table utility implements the standardized engineering formulation:
Standardized parametric evaluation for UNC / UNF Thread Reference TableComplete UNC (coarse) and UNF (fine) thread table: #0 through 1-1/2 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
Ensure clearance hole diameters conform to ISO 273 / ASME B18.2.8 medium fit series and verify minimum thread engagement length (typically 1.0×d in steel, 2.0×d in aluminum) in your assembly BOM.
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 UNC / UNF Thread Reference Table
What governing equation and methodology does the UNC / UNF Thread Reference Table use?
The UNC / UNF Thread Reference Table evaluates complete unc (coarse) and unf (fine) thread table: #0 through 1-1/2 within the Fastener Engineering & Bolted Joint Mechanics domain using the governing formulation: Standardized parametric evaluation for UNC / UNF Thread Reference Table. 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 UNC / UNF Thread Reference Table calculations?
Calculations and boundary assumptions in this utility align with recognized industry references including VDI 2230 (Systematic Calculation of High Duty Bolted Joints), ISO 898-1 (Mechanical Properties of Carbon & Alloy Steel Fasteners), ASME B1.1 / ISO 68-1. 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 UNC / UNF Thread Reference Table into my CAD or BIM workflow?
Ensure clearance hole diameters conform to ISO 273 / ASME B18.2.8 medium fit series and verify minimum thread engagement length (typically 1.0×d in steel, 2.0×d in aluminum) in your assembly BOM. Using the baseline benchmark (standard nominal boundary parameters for UNC / UNF Thread Reference Table), the solver yields verified design compliance metrics for UNC / UNF Thread Reference Table, which can be directly cross-referenced against your parametric 3D assembly constraints, 2D fabrication drawings, or bill of materials (BOM).