Figuring out the exact tap drill size or minor diameter for a specific thread specification during a design workflow requires immediate, accurate data. Guessing the clearance hole or mixing up a metric thread chart with a UNC thread chart leads to stripped parts, cross-threading, and costly rework on the shop floor. Managing thousands of rapid prototyping and CNC machining orders has allowed us to compile the exact standard dimensions needed to prevent assembly interference. For engineers and procurement specialists verifying CAD models or validating hardware sourcing, the thread size charts below provide the exact major diameters, minor diameters, and tap drill sizes required for your next build.
| Thread Size | TPI / Pitch | Major Dia | Minor Dia | Tap Drill |
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This interactive thread dimensions chart allows you to instantly filter by thread standard (UNC, UNF, Metric) to find the exact pitch, major diameter, and required tap drill size for your specifications. Input your desired thread size to generate the required tolerances and machining parameters automatically.
Unified National Thread Sizes Chart (UNC / UNF / UNEF)
The Unified Thread Standard (UTS) is the primary thread specification used in North America. These charts integrate the core dimensions, thread counts, and matching tap drill diameters into a single, comprehensive reference for your shop floor. All dimensions are in inches.
Machine Screw Sizes (#0 to #12)
Use this thread diameter chart for small-scale electronics, consumer products, and precision instrumentation.
| Thread Size | Thread Type | TPI | Major Diameter (in) | Minor Diameter (in) | Recommended Tap Drill (in) |
| 0-80 | UNF | 80 | 0.060 | 0.047 | 0.052 |
| 1-64 | UNC | 64 | 0.073 | 0.056 | 0.0625 |
| 2-56 | UNC | 56 | 0.086 | 0.067 | 0.073 |
| 2-64 | UNF | 64 | 0.086 | 0.069 | 0.076 |
| 4-40 | UNC | 40 | 0.112 | 0.085 | 0.089 |
| 5-40 | UNC | 40 | 0.125 | 0.098 | 0.1015 |
| 5-44 | UNF | 44 | 0.125 | 0.100 | 0.104 |
| 6-32 | UNC | 32 | 0.136 | 0.104 | 0.1065 |
| 6-40 | UNF | 40 | 0.136 | 0.111 | 0.113 |
| 8-32 | UNC | 32 | 0.164 | 0.130 | 0.136 |
| 8-36 | UNF | 36 | 0.164 | 0.134 | 0.136 |
| 10-24 | UNC | 24 | 0.190 | 0.145 | 0.1495 |
| 10-32 | UNF | 32 | 0.190 | 0.156 | 0.159 |
| 12-24 | UNC | 24 | 0.216 | 0.171 | 0.177 |
| 12-28 | UNF | 28 | 0.216 | 0.180 | 0.181 |
| 12-32 | UNEF | 32 | 0.216 | 0.185 | 0.189 |
Fractional Sizes (1/4″ to 1″)
This bolt thread dimensions chart covers the standard fractional sizes used in heavy machinery, automotive components, and structural assemblies.
| Thread Size | Thread Type | TPI | Major Diameter (in) | Minor Diameter (in) | Recommended Tap Drill (in) |
| 1/4-20 | UNC | 20 | 0.250 | 0.196 | 0.201 |
| 1/4-28 | UNF | 28 | 0.250 | 0.211 | 0.213 |
| 1/4-32 | UNEF | 32 | 0.250 | 0.218 | 0.2187 |
| 5/16-18 | UNC | 18 | 0.313 | 0.252 | 0.257 |
| 5/16-24 | UNF | 24 | 0.313 | 0.267 | 0.272 |
| 5/16-32 | UNEF | 32 | 0.313 | 0.279 | 0.2812 |
| 3/8-16 | UNC | 16 | 0.375 | 0.307 | 0.3125 |
| 3/8-24 | UNF | 24 | 0.375 | 0.330 | 0.332 |
| 3/8-32 | UNEF | 32 | 0.375 | 0.342 | 0.3437 |
| 7/16-14 | UNC | 14 | 0.438 | 0.360 | 0.368 |
| 7/16-20 | UNF | 20 | 0.438 | 0.383 | 0.3906 |
| 7/16-28 | UNEF | 28 | 0.438 | 0.401 | 0.4062 |
| 1/2-13 | UNC | 13 | 0.500 | 0.417 | 0.4219 |
| 1/2-20 | UNF | 20 | 0.500 | 0.446 | 0.4531 |
| 1/2-28 | UNEF | 28 | 0.500 | 0.464 | 0.4687 |
| 9/16-12 | UNC | 12 | 0.563 | 0.472 | 0.4844 |
| 9/16-18 | UNF | 18 | 0.563 | 0.502 | 0.5156 |
| 9/16-24 | UNEF | 24 | 0.563 | 0.518 | 0.5312 |
| 5/8-11 | UNC | 11 | 0.625 | 0.527 | 0.5312 |
| 5/8-18 | UNF | 18 | 0.625 | 0.565 | 0.5781 |
| 5/8-24 | UNEF | 24 | 0.625 | 0.581 | 0.5937 |
| 3/4-10 | UNC | 10 | 0.750 | 0.642 | 0.6562 |
| 3/4-16 | UNF | 16 | 0.750 | 0.682 | 0.6875 |
| 3/4-20 | UNEF | 20 | 0.750 | 0.701 | 0.7031 |
| 7/8-9 | UNC | 9 | 0.875 | 0.755 | 0.7656 |
| 7/8-14 | UNF | 14 | 0.875 | 0.798 | 0.8125 |
| 7/8-20 | UNEF | 20 | 0.875 | 0.826 | 0.8281 |
| 1-8 | UNC | 8 | 1.000 | 0.865 | 0.875 |
| 1-14 | UNF | 14 | 1.000 | 0.910 | 0.9375 |
| 1-20 | UNEF | 20 | 1.000 | 0.938 | 0.9531 |
Pro Tip: When designing clearance holes for these standard bolts, add 0.01″ to 0.03″ to the major diameter. This provides adequate clearance for standard assembly without requiring custom adjustments.
Metric Thread Size Chart
Global supply chains rely on metric standards. A metric bolt thread chart identifies the outer diameter and the specific pitch (the distance between individual threads).
| Metric Size | Standard Pitch (mm) | Standard Tap Drill (mm) | Fine Pitch (mm) | Fine Tap Drill (mm) |
| M2 | 0.40 | 1.60 | – | – |
| M2.5 | 0.45 | 2.05 | – | – |
| M3 | 0.50 | 2.50 | – | – |
| M4 | 0.70 | 3.30 | – | – |
| M5 | 0.80 | 4.20 | – | – |
| M6 | 1.00 | 5.00 | 0.75 | 5.20 |
| M8 | 1.25 | 6.80 | 1.00 | 7.00 |
| M10 | 1.50 | 8.50 | 1.25 | 8.80 |
| M12 | 1.75 | 10.20 | 1.25 | 10.80 |
Refer to this m thread size chart when converting designs from inch to metric. The pitch values dictate the exact tap drill required for a 75% thread engagement.
Pipe Thread Dimensions Chart (NPT and BSP)
Fluid and gas management systems require specific thread tapers to maintain seals. The national pipe thread size chart (NPT) differs significantly from standard mechanical fasteners.
NPT Thread Chart (National Pipe Taper)
An NPT thread diameter chart is critical for plumbing and pneumatic applications. The NPT designation refers to the nominal inside diameter of the pipe, not the physical outer diameter of the thread.
| Nominal Size | TPI | O.D. of Pipe (in) | Tap Drill Size (in) |
| 1/8″ | 27 | 0.405 | 11/32 |
| 1/4″ | 18 | 0.540 | 7/16 |
| 3/8″ | 18 | 0.675 | 37/64 |
| 1/2″ | 14 | 0.840 | 23/32 |
| 3/4″ | 14 | 1.050 | 59/64 |
| 1″ | 11.5 | 1.315 | 1-5/32 |
For European and international piping systems, you must reference a british standard pipe thread chart. BSP comes in two variants: BSPP (parallel) and BSPT (tapered). A pipe thread drill and tap chart for BSP components requires entirely different tooling than NPT.
Specialty Thread Standards Used in Industrial Applications
Not all applications fit into standard UNC or Metric profiles. Aerospace, hydraulics, and linear motion control systems require specialized threads.
- AN Thread Size Chart: Used extensively in aerospace and automotive fluid lines. AN (Army-Navy) threads use a 37-degree flare fitting for high-pressure seals.
- JIC Thread Size Chart: Functionally identical to AN threads but manufactured to slightly looser industrial tolerances. Both use UNF thread pitches.
- Acme Screw Thread Chart: Designed for power transmission rather than fastening. Acme threads have a trapezoidal profile to carry heavy axial loads in devices like lead screws and CNC actuators.
Key Thread Measurement Terminology Explained
Understanding a thread and pitch chart requires clear definitions of machining terms.
- TPI (Threads Per Inch): A higher TPI value means the threads are finer and more tightly packed. In a single size category, TPI increases from UNC, to UNF, to UNEF.
- Major Diameter: The largest outside diameter of an external thread. This is the nominal size listed on a bolt size and thread chart.
- Minor Diameter: The smallest diameter of an internal thread. This measurement determines the core strength of the fastener.
- Tap Drill Diameter: The preliminary hole size required before using a tapping tool. Drilling to this exact size ensures the tap cuts standard thread profiles without snapping.
Design for Manufacturability (DFM) for Tapped Holes
Proper thread specification goes beyond referencing a tap and thread chart. You must optimize the geometry for the CNC machining process.
- Prioritize UNC (Coarse): Coarse threads are easier to machine, less prone to cross-threading, and ideal for general assembly. Use them by default.
- Use UNF (Fine) Strategically: Fine threads provide better resistance to vibration and allow for more precise positional adjustments. Specify them for automotive, hydraulic, or thin-walled applications.
- Limit UNEF (Extra Fine): Use extra-fine threads only in precision instruments or extremely constrained spaces. They are not recommended for components requiring frequent assembly and disassembly.
RapidDirect provides full-cycle NPI services, coordinating multiple processes like 3/4/5-Axis milling and turning within a single project. Our intelligent online platform offers instant quoting and free DFM reports, automatically checking your CAD models against standard machining constraints.
When you specify a thread size, our CNC standard tolerance guarantees ISO 2768-m (+/- 0.1mm), with precision tolerances up to +/- 0.01mm available upon request. You can upload your STEP file directly to RapidDirect to get manufacturing feedback and pricing in minutes.
Frequently Asked Questions About Thread Size Charts
Select UNC for general mechanical structures due to high machining efficiency and durability. Choose UNF for automotive and hydraulic applications where vibration resistance and sealing are critical. Reserve UNEF for precision instrumentation and very thin-walled parts.
Yes. Processes like anodizing, electroplating, and powder coating add material to the part surface. You must mask threaded holes prior to finishing or account for the coating thickness during the tapping phase to ensure fasteners still fit.
If the tap drill is too small, the tapping tool will likely break inside the part due to excessive torque. If the tap drill is too large, the resulting threads will be shallow, leading to a weak joint that strips easily under load.
A general rule of thumb is to drill the hole depth to at least 1.5 times the major diameter of the thread. You must also allow extra clearance at the bottom of a blind hole for chips to evacuate during the tapping process.
Optimize Your Hardware Sourcing
Mismatched threads and incorrect tolerances bring assembly lines to a halt. Verifying your CAD models against a reliable thread size chart is the first step toward a successful build.
RapidDirect automates this validation process for engineers and procurement managers. Our platform analyzes your parts, flags DFM issues, and provides an instant quote in minutes. Log in to the RapidDirect platform today to upload your files, review your thread specifications, and secure fast, accurate manufacturing for your next project.
