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UNC THREAD CHART

Use this UNC thread chart to look up unified coarse thread dimensions per ASME B1.1. Find major diameter, pitch diameter and minor diameter limits for both external (2A/3A) and internal (2B/3B) threads.

External chart + calculator Internal chart + calculator FAQ

Popular lookups: 1/4-20 thread dimensions, 1/2-13 thread dimensions, 3/4-10 thread dimensions, 1-8 UNC thread dimensions, 4-40 major/minor diameter, 2-56 major diameter, 6-32 minor diameter.

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External Thread Dimensions for UNC Screw Threads:

UNC External Thread Calculator

Select a size (for example 1/4-20 or 4-40) and a tolerance class (2A/3A) to show limiting diameters.

Calculator reads values directly from the external thread chart below.
Nominal TPI Class d max d min d2 max d2 min Minor Dia. max
— — — — — — — —
UNC Thread Chart — External Thread Dimensions (ASME B1.1)
Nominal
Diameter		 TPI Tolerance
Class		 Major Diameter Pitch Diameter Minor Diameter
max.
d max. d min. d2 max. d2 min.
Nominal
Diameter		 TPI Tolerance
Class		 Major Dia. Pitch Dia. Max.
Minor
Diameter
max. min. max. min.
#1 - 64 64 2A 0.0724 0.0686 0.0623 0.0603 0.0538
#2 - 56 56 2A 0.0854 0.0813 0.0738 0.0717 0.0642
#3 - 48 48 2A 0.0983 0.0938 0.0848 0.0825 0.0734
#4- 40 40 2A 0.1112 0.1061 0.0950 0.0925 0.0814
#5 - 40 40 2A 0.1242 0.1191 0.1080 0.1054 0.0944
#6 - 32 32 2A 0.1372 0.1312 0.1169 0.1141 0.1000
#8 - 32 32 2A 0.1631 0.1571 0.1428 0.1399 0.1259
#10 - 24 24 2A 0.1890 0.1818 0.1619 0.1586 0.1394
#12 - 24 24 2A 0.2150 0.2078 0.1879 0.1845 0.1654
1/4” - 20 20 2A 0.2489 0.2408 0.2164 0.2127 0.1894
5/16" - 18 18 2A 0.3113 0.3026 0.2752 0.2712 0.2452
3/8" - 16 16 2A 0.3737 0.3643 0.3331 0.3287 0.2992
7/16" - 14 14 2A 0.4361 0.4258 0.3897 0.3850 0.3511
1/2" - 13 13 2A 0.4985 0.4876 0.4485 0.4435 0.4069
Nominal
Diameter		 TPI Tolerance
Class		 Major Dia. Pitch Dia. Max.
Minor
Diameter
max. min. max. min.
9/16" - 12 12 2A 0.5609 0.5495 0.5068 0.5016 0.4617
5/8" - 11 11 2A 0.6234 0.6113 0.5644 0.5589 0.5152
3/4" - 10 10 2A 0.7482 0.7353 0.6832 0.6773 0.6291
7/8" - 9 9 2A 0.8731 0.8592 0.8009 0.7946 0.7408
1" - 8 8 2A 0.9980 0.9830 0.9168 0.9100 0.8492
1 1/8" - 7 7 2A 1.1228 1.1064 1.0300 1.0228 0.9527
1 1/4" - 7 7 2A 1.2478 1.2314 1.1550 1.1476 1.0777
1 3/8" - 6 6 2A 1.3726 1.3544 1.2643 1.2563 1.1742
1 1/2" - 6 6 2A 1.4976 1.4794 1.3893 1.3812 1.2992
1 3/4" - 5 5 2A 1.7473 1.7268 1.6174 1.6085 1.5092
2" - 4 1/2 4.5 2A 1.9971 1.9751 1.8528 1.8433 1.7324
2 1/4" - 4 1/2 4.5 2A 2.2471 2.2251 2.1028 2.0931 1.9824
2 1/2" - 4 4 2A 2.4969 2.4731 2.3345 2.3241 2.1992
2 3/4" - 4 4 2A 2.7468 2.7230 2.5844 2.5739 2.4491
3" - 4 4 2A 2.9968 2.9730 2.8344 2.8237 2.6991
3 1/4" - 4 4 2A 3.2467 3.2229 3.0843 3.0734 2.9490
3 1/2" - 4 4 2A 3.4967 3.4729 3.3343 3.3233 3.1990
3 3/4" - 4 4 2A 3.7466 3.7228 3.5842 3.5730 3.4489
4" - 4 4 2A 3.9966 3.9728 3.8342 3.8229 3.6989
Nominal
Diameter		 TPI Tolerance
Class		 max. min. max. min. Max.
Minor
Diameter
Major Dia. Pitch Dia.
 

Internal Thread Dimensions for UNC Screw Threads:

UNC Internal Thread Calculator

Use this for internal threads (for example UNC-2B / UNC-3B) to see D, D2 and D1 limits.

Calculator reads values directly from the internal thread chart below.
Nominal TPI Class D min D2 max D2 min D1 max D1 min
— — — — — — — —
UNC Thread Chart — Internal Thread Dimensions (ASME B1.1)
Nominal
Diameter		 TPI Tolerance
Class		 Major Diameter Pitch Diameter Minor Diameter
D min. D2 max. D2 min. D1 max. D1 min.
Nominal
Diameter		 TPI Tolerance
Class		 Major Dia. Pitch Dia. Minor Dia.
min. max. min. max.  min
#1 - 64 64 2B 0.0730 0.0655 0.0629 0.0623 0.0561
#2 - 56 56 2B 0.0860 0.0772 0.0744 0.0737 0.667
#3 - 48 48 2B 0.0990 0.0855 0.0855 0.0845 0.0764
#4- 40 40 2B 0.1120 0.0991 0.0958 0.0939 0.0849
#5 - 40 40 2B 0.1250 0.1121 0.1088 0.1062 0.0979
#6 - 32 32 2B 0.1380 0.1214 0.1177 0.1140 0.1040
#8 - 32 32 2B 0.1640 0.1475 0.1437 0.1390 0.1300
#10 - 24 24 2B 0.1900 0.1672 0.1629 0.1560 0.1450
#12 - 24 24 2B 0.2160 0.1933 0.1889 0.1810 0.1710
1/4” - 20 20 2B 0.2500 0.2224 0.2175 0.2070 0.1960
5/16" - 18 18 2B 0.3125 0.2817 0.2764 0.2650 0.2520
3/8" - 16 16 2B 0.3750 0.3401 0.3344 0.3210 0.3070
7/16" - 14 14 2B 0.4375 0.3972 0.3911 0.3760 0.3600
1/2" - 13 13 2B 0.5000 0.4565 0.4500 0.4340 0.4170
Nominal
Diameter		 TPI Tolerance
Class		 Major Dia. Pitch Dia. Minor Dia.
min. max. min. max. min.
9/16" - 12 12 2B 0.5625 0.5125 0.5084 0.4900 0.4720
5/8" - 11 11 2B 0.6250 0.5732 0.5660 0.5460 0.5270
3/4" - 10 10 2B 0.7500 0.6927 0.6850 0.6630 0.6420
7/8" - 9 9 2B 0.8750 0.8110 0.8028 0.7780 0.7550
1" - 8 8 2B 1.0000 0.9276 0.9188 0.8900 0.8650
1 1/8" - 7 7 2B 1.1250 1.0416 1.0322 0.9980 0.9700
1 1/4" - 7 7 2B 1.2500 1.1668 1.1572 1.1230 1.0950
1 3/8" - 6 6 2B 1.3750 1.2771 1.2667 1.2250 1.1950
1 1/2" - 6 6 2B 1.5000 1.4075 1.3917 1.3500 1.3200
1 3/4" - 5 5 2B 1.7500 1.6317 1.6201 1.5680 1.5340
2" - 4 1/2 4.5 2B 2.0000 1.8681 1.8557 1.7950 1.7590
2 1/4" - 4 1/2 4.5 2B 2.2500 2.1183 2.1057 2.0450 2.0090
2 1/2" - 4 4 2B 2.5000 2.3511 2.3376 2.2670 2.2290
2 3/4" - 4 4 2B 2.7500 2.6013 2.5876 2.5170 2.4790
3" - 4 4 2B 3.0000 2.8515 2.8376 2.7670 2.7290
3 1/4" - 4 4 2B 3.2500 3.1017 3.0876 3.0170 2.9790
3 1/2" - 4 4 2B 3.5000 3.3519 3.3376 3.2670 3.2290
3 3/4" - 4 4 2B 3.7500 3.6021 3.5876 3.5170 3.4790
4" - 4 4 2B 4.0000 3.8523 3.8376 3.7670 3.7290
Nominal
Diameter		 TPI Tolerance
Class		 min. max. min. max. min.
Major Dia. Pitch Dia. Minor Dia.

General Note: All dimensions expressed in inches.

Supplements:

Reference:

  • ASME B1.1-2003, Unified Inch Screw Threads (UN and UNR Thread Form)
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2016) . Machinery's Handbook . 30th edition.  Industrial Press Inc.
  • Oberg, E. , Jones ,F.D. , Horton H.L. , Ryffel H.H., (2012) . Machinery's Handbook . 29th edition.  Industrial Press Inc.

FAQ

What are the dimensions for a 1/4-20 UNC thread?

Choose 1/4-20 in the calculator above. Use the external chart for bolts/screws (2A/3A) and the internal chart for nuts/tapped holes (2B/3B). The results list major, pitch and minor diameter limits per ASME B1.1.

What is the major diameter for 4-40 UNC?

Filter the external chart by selecting #4-40 in the calculator (or scroll in the chart). The major diameter is shown as d max and d min. For internal threads, use the internal chart to see D min.

What does UNC-2B mean?

2B is a common internal-thread tolerance class. Use the internal calculator to view pitch diameter (D2) and minor diameter (D1) limits for 2B.

Need tap drill size for common UNC threads (2-56, 4-40, 6-32, 8-32, 1/4-20)?

Use the tap drill size calculator for recommended drill sizes and tapping data.