UNC and UNF - Unified Inch Screw Threads
- UNC – Unified National Coarse Thread - comparable with the ISO metric thread
- UNF – Unified National Fine Thread
- Female and Male UNC/UNF threads are both parallel
- The UNC/UNF flank angle is 60°
Unified threads comes in three different classes:
- for applications where a liberal tolerance is required to permit easy assembly even with slightly nicked threads
- most commonly used class for general applications
- for applications where closeness of fit and/or accuracy of thread elements are important
UNC - Unified Coarse Threads
UNC threads according ANSI B1.1:
| Major Diameter (in) | Threads per inch (tpi) | Major Diameter | Tap Drill Size (mm) | Pitch (mm) | |
|---|---|---|---|---|---|
| (in) | (mm) | ||||
| #1 - 64 | 64 | 0.073 | 1.854 | 1.50 | 0.397 |
| #2 - 56 | 56 | 0.086 | 2.184 | 1.80 | 0.453 |
| #3 - 48 | 48 | 0.099 | 2.515 | 2.10 | 0.529 |
| #4 - 40 | 40 | 0.112 | 2.845 | 2.35 | 0.635 |
| #5 - 40 | 40 | 0.125 | 3.175 | 2.65 | 0.635 |
| #6 - 32 | 32 | 0.138 | 3.505 | 2.85 | 0.794 |
| #8 - 32 | 32 | 0.164 | 4.166 | 3.50 | 0.794 |
| #10 - 24 | 24 | 0.190 | 4.826 | 4.00 | 1.058 |
| #12 - 24 | 24 | 0.216 | 5.486 | 4.65 | 1.058 |
| 1/4" - 20 | 20 | 0.250 | 6.350 | 5.35 | 1.270 |
| 5/16" - 18 | 18 | 0.313 | 7.938 | 6.80 | 1.411 |
| 3/8" - 16 | 16 | 0.375 | 9.525 | 8.25 | 1.587 |
| 7/16" - 14 | 14 | 0.438 | 11.112 | 9.65 | 1.814 |
| 1/2" - 13 | 13 | 0.500 | 12.700 | 11.15 | 1.954 |
| 9/16" - 12 | 12 | 0.563 | 14.288 | 12.60 | 2.117 |
| 5/8" - 11 | 11 | 0.625 | 15.875 | 14.05 | 2.309 |
| 3/4" - 10 | 10 | 0.750 | 19.050 | 17.00 | 2.540 |
| 7/8" - 9 | 9 | 0.875 | 22.225 | 20.00 | 2.822 |
| 1" - 8 | 8 | 1.000 | 25.400 | 22.85 | 3.175 |
| 1 1/8" - 7 | 7 | 1.125 | 28.575 | 25.65 | 3.628 |
| 1 1/4" - 7 | 7 | 1.250 | 31.750 | 28.85 | 3.628 |
| 1 3/8" - 6 | 6 | 1.375 | 34.925 | 31.55 | 4.233 |
| 1 1/2" - 6 | 6 | 1.500 | 38.100 | 34.70 | 4.233 |
| 1 3/4" - 5 | 5 | 1.750 | 44.450 | 40.40 | 5.080 |
| 2" - 4 1/2 | 4 1/2 | 2.000 | 50.800 | 46.30 | 5.644 |
| 2 1/4" - 4 1/2 | 4 1/2 | 2.250 | 57.150 | 52.65 | 5.644 |
| 2 1/2" - 4 | 4 | 2.500 | 63.500 | 58.50 | 6.350 |
| 2 3/4" - 4 | 4 | 2.750 | 69.850 | 64.75 | 6.350 |
| 3" - 4 | 4 | 3.000 | 76.200 | 71.10 | 6.350 |
| 3 1/4" - 4 | 4 | 3.250 | 82.550 | 77.45 | 6.350 |
| 3 1/2" - 4 | 4 | 3.500 | 88.900 | 83.80 | 6.350 |
| 3 3/4" - 4 | 4 | 3.750 | 95.250 | 90.15 | 6.350 |
| 4" - 4 | 4 | 4.000 | 101.600 | 96.50 | 6.350 |
Example - Typical designation of an UNC thread
- 1/4” x 20 UNC
UNF - Unified National Fine Threads
UNF threads ANSI B1.1:
| Major Diameter (in) | Threads per inch (tpi) | Major Diameter | Tap Drill Size (mm) | Pitch (mm) | |
|---|---|---|---|---|---|
| (in) | (mm) | ||||
| #0 - 80 | 80 | 0.060 | 1.524 | 1.25 | 0.317 |
| #1 - 72 | 72 | 0.073 | 1.854 | 1.55 | 0.353 |
| #2 - 64 | 64 | 0.086 | 2.184 | 1.90 | 0.397 |
| #3 - 56 | 56 | 0.099 | 2.515 | 2.15 | 0.453 |
| #4 - 48 | 48 | 0.112 | 2.845 | 2.40 | 0.529 |
| #5 - 44 | 44 | 0.125 | 3.175 | 2.70 | 0.577 |
| #6 - 40 | 40 | 0.138 | 3.505 | 2.95 | 0.635 |
| #8 - 36 | 36 | 0.164 | 4.166 | 3.50 | 0.705 |
| #10 - 32 | 32 | 0.190 | 4.826 | 4.10 | 0.794 |
| #12 - 28 | 28 | 0.216 | 5.486 | 4.70 | 0.907 |
| 1/4" - 28 | 28 | 0.250 | 6.350 | 5.50 | 0.907 |
| 5/16" - 24 | 24 | 0.313 | 7.938 | 6.90 | 1.058 |
| 3/8" - 24 | 24 | 0.375 | 9.525 | 8.50 | 1.058 |
| 7/16" - 20 | 20 | 0.438 | 11.112 | 9.90 | 1.270 |
| 1/2" - 20 | 20 | 0.500 | 12.700 | 11.50 | 1.270 |
| 9/16" - 18 | 18 | 0.563 | 14.288 | 12.90 | 1.411 |
| 5/8" - 18 | 18 | 0.625 | 15.875 | 14.50 | 1.411 |
| 3/4" - 16 | 16 | 0.750 | 19.050 | 17.50 | 1.587 |
| 7/8" - 14 | 14 | 0.875 | 22.225 | 20.40 | 1.814 |
| 1" - 12 | 12 | 1.000 | 25.400 | 23.25 | 2.117 |
| 1 1/8" - 12 | 12 | 1.125 | 28.575 | 26.50 | 2.117 |
| 1 1/4" - 12 | 12 | 1.250 | 31.750 | 29.50 | 2.117 |
| 1 3/8" - 12 | 12 | 1.375 | 34.925 | 32.75 | 2.117 |
| 1 1/2" - 12 | 12 | 1.500 | 38.100 | 36.00 | 2.117 |
Example - Typical designation of an UNF thread
- 1/2” x 20 UNF
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