Thread standards are essential in mechanical manufacturing, especially in industries such as machinery, hydraulic systems, and stainless steel pipe fittings.
American threads, also known as Unified Threads, are widely used in North America and many international industrial applications.
The Unified Thread Standard mainly includes:
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UNC – Unified National Coarse
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UNF – Unified National Fine
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UNEF – Unified National Extra Fine
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NPT – National Pipe Thread
As a professional pipe fitting factory , we must need study and clear about the thread drill size then make sure the thread satisfy Go/No-Go Gauge Specifications. Based on different type
During the cnc machinery steups , there are 2 ways to get the thread :
A- Thread cnc machinery by the cnc cutter .
B-Drill the hole then produce by tapping Machine Operation
The following charts summarize common American thread drilling sizes used in engineering and manufacturing.
UNC Thread Drill Size Chart (Unified National Coarse)
| Thread Size | Standard Diameter (mm) | Tap Drill Size (mm) | Max | Min |
|---|---|---|---|---|
| No.1-64 | 1.854 | 1.55 | 1.582 | 1.425 |
| No.2-56 | 2.184 | 1.80 | 1.871 | 1.695 |
| No.3-48 | 2.515 | 2.10 | 2.146 | 1.941 |
| No.4-40 | 2.845 | 2.30 | 2.385 | 2.157 |
| No.5-40 | 3.175 | 2.60 | 2.697 | 2.487 |
| No.6-32 | 3.505 | 2.80 | 2.895 | 2.642 |
| No.8-32 | 4.166 | 3.40 | 3.530 | 3.302 |
| No.10-24 | 4.826 | 3.90 | 3.962 | 3.683 |
| No.12-24 | 5.486 | 4.50 | 4.597 | 4.344 |
| 1/4-20 | 6.350 | 5.10 | 5.257 | 4.979 |
| 5/16-18 | 7.940 | 6.60 | 6.731 | 6.401 |
| 3/8-16 | 9.525 | 8.00 | 8.153 | 7.798 |
| 7/16-14 | 11.112 | 9.40 | 9.550 | 9.144 |
| 1/2-13 | 12.700 | 10.80 | 11.023 | 10.592 |
| 9/16-12 | 14.288 | 12.20 | 12.446 | 11.989 |
| 5/8-11 | 15.875 | 13.60 | 13.868 | 13.386 |
| 3/4-10 | 19.050 | 16.50 | 16.840 | 16.307 |
UNF Thread Drill Size Chart (Unified National Fine)
| Thread Size | Standard Diameter (mm) | Tap Drill Size (mm) | Max | Min |
|---|---|---|---|---|
| No.0-80 | 1.524 | 1.25 | 1.305 | 1.182 |
| No.1-72 | 1.854 | 1.55 | 1.612 | 1.474 |
| No.2-64 | 2.184 | 1.85 | 1.912 | 1.756 |
| No.3-56 | 2.515 | 2.10 | 2.197 | 2.025 |
| No.4-48 | 2.845 | 2.40 | 2.458 | 2.271 |
| No.5-44 | 3.175 | 2.70 | 2.740 | 2.551 |
| No.6-40 | 3.505 | 2.90 | 3.022 | 2.820 |
| No.8-36 | 4.166 | 3.50 | 3.606 | 3.404 |
| No.10-32 | 4.826 | 4.10 | 4.165 | 3.963 |
| No.12-28 | 5.846 | 4.60 | 4.724 | 4.496 |
| 1/4-28 | 6.350 | 5.50 | 5.588 | 5.360 |
| 5/16-24 | 7.940 | 6.90 | 7.035 | 6.782 |
| 3/8-24 | 9.525 | 8.50 | 8.636 | 8.382 |
| 7/16-20 | 11.112 | 9.90 | 10.033 | 9.729 |
| 1/2-20 | 12.700 | 11.50 | 11.607 | 11.329 |
UNEF Thread Drill Size Chart (Unified National Extra Fine)
| Thread Size | Standard Diameter (mm) | Tap Drill Size (mm) | Max | Min |
|---|---|---|---|---|
| No.12-32 | 4.70 | 4.826 | 4.623 | |
| 1/4-32 | 5.60 | 5.690 | 5.486 | |
| 5/16-32 | 7.10 | 7.264 | 7.087 | |
| 3/8-32 | 8.70 | 8.865 | 8.661 | |
| 7/16-28 | 10.20 | 10.338 | 10.135 | |
| 1/2-28 | 11.80 | 11.938 | 11.709 |
NPT Pipe Thread Drill Size Chart
| Thread Size | Drill Size (mm) with Reamer | Without Reamer |
|---|---|---|
| 1/16-27 | 6.10 | 6.25 |
| 1/8-27 | 8.33 | 8.43 |
| 1/4-18 | 10.72 | 11.13 |
| 3/8-18 | 14.27 | 14.68 |
| 1/2-14 | 17.48 | 18.26 |
| 3/4-14 | 22.63 | 23.42 |
Applications in Stainless Steel Pipe Fittings Manufacturing
Thread accuracy is extremely important when producing stainless steel pipe fittings. Many industrial components rely on threaded connections to ensure leak-free sealing and reliable assembly.
Typical products that use these threads include:
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hydraulic adapters
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hose fittings ,adaper fitting
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instrumentation fittings
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threaded connectors
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custom CNC turning parts
As a stainless steel pipe fittings supplier, our factory specializes in cnc turning and cnc machinery by cnc lathe machine. We support batch production according to 2D drawings, 3D models, or samples to satisfy customer demand .
Our manufacturing capabilities include:
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Monthly production capacity: 300,000 pieces
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MOQ for custom parts: 2000 pieces for small batch , this type usually produce by the bar or stock tube . For complex type stainless steel fitting or carbon steel fittings , based on hot forging or cold heading , the moq quantity is based on the blank demand will demand more quantity .
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Materials:201, 304, 316, 303 stainless steel and carbon steel(1020,1008,1010,1035,1045, Q235,42CRMO .40CR etc ) , carbon steel have more different types material grade .
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Surface treatments: polishing, passivation, plating, sandblasting
FAQ – American Thread Standards
What is the difference between UNC and UNF threads?
UNC (Unified National Coarse) threads have larger thread spacing, making them easier to assemble and more resistant to damage.
UNF (Unified National Fine) threads have smaller spacing, which provides better strength and vibration resistance.
Where are American threads commonly used?
American thread standards are widely used in:
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hydraulic systems
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automotive components
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aerospace equipment
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industrial machinery
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stainless steel pipe fittings
Why are correct tap drill sizes important?
Using the correct tap drill size ensures that the thread profile is formed accurately. Incorrect drilling sizes can lead to:
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weak threads
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assembly difficulties
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leakage in pipe connections
Can stainless steel threads be CNC machined?
Yes. Most stainless steel threaded parts are produced using CNC turning machines. This process provides better dimensional accuracy and surface quality compared with traditional machining.
