Note: Standard fractional end-mills can be purchased from MSC Industrial Supply.
            Decimal end-mills can be purchased from Harvey Tool.
            Metric end-mills can be purchased from Melin Tool Company. (catalog)

UNIFIED SCREW THREADS (CLASS 2A & 2B)

EXTERNAL (CLASS 2A)
 
INTERNAL (CLASS 2A)
Thread Size
Allowance
Major Diameter
Max          Min
Minor Dia.

Minor Diameter
Max         Min

Major Dia.   Min
0-80 UNF
0.0005
0.0595      0.0563
0.0442
0.0465      0.0514
0.0600
1-64 UNC
0.0006
0.0724      0.0686
0.0532
0.0561      0.0623
0.0730
1-72 UNF
0.0006
0.0724      0.0689
0.0554
0.0580      0.0635
0.0730
2-56 UNC
0.0006
0.0854      0.0813
0.0635
0.0667      0.0737
0.0860
2-64 UNF
0.0006
0.0854      0.0816
0.0662
0.0691      0.0753
0.0860
3-48 UNC
0.00070.0764
0.0797      0.0865
0.0990
4-40 UNC
0.0008
0.1112      0.1061
0.0805
0.0849      0.0939
0.1120
4-48 UNF
0.0007
0.1113      0.1068
0.0857
0.0894      0.0968
0.1120
5-40 UNC
0.0008
0.1242      0.1191
0.0935
0.0979      0.1062
0.1250
5-44 UNF
0.0007
0.1243      0.1195
0.0964
0.1004      0.1079
0.1250
6-32 UNC
0.0008
0.1372      0.1312
0.0989
0.104      0.114
0.1380
6-40 UNF
0.0008
0.1372      0.1321
0.1065
0.111      0.119
0.1380
8-32 UNC
0.0009
0.1631      0.1571
0.1248
0.130      0.139
0.1640
8-36 UNF
0.0008
0.1632      0.1577
0.1291
0.134      0.142
0.1640
10-24 UNC
0.0010
0.1890      0.1818
0.1379
0.145      0.156
0.1900
10-28 UNS
0.0010
0.1890      0.1825
0.1452
0.151      0.160
0.1900
10-32 UNF
0.0009
0.1891      0.1831
0.1508
0.156      0.164
0.1900
10-36 UNS
0.0009
0.1891      0.1836
0.1550
0.160      0.166
0.1900
10-40 UNS
0.0009
0.1891      0.1840
0.1584
0.163      0.169
0.1900
10-48 UNS
0.0008
0.1892      0.1847
0.1636
0.167      0.172
0.1900
10-56 UNS
0.0007
0.1893      0.1852
0.1674
0.171      0.175
0.1900
12-24 UNC
0.0010
0.2150      0.2078
0.1639
0.171      0.181
0.2160
12-28 UNF
0.0010
0.2150      0.2085
0.1712
0.177      0.186
0.2160
12-32 UNEF
0.0009
0.2151      0.2091
0.1768
0.182      0.190
0.2160
12-36 UNS
0.0009
0.2151      0.2096
0.1810
0.186      0.192
0.2160
12-40 UNS
0.0009
0.2151      0.2100
0.1844
0.189      0.195
0.2160
12-48 UNS
0.0008
0.2152      0.2107
0.1896
0.193      0.198
0.2160
12-56 UNS
0.0007
0.2153      0.2112
0.1934
0.197      0.201
0.2160
1/4-20 UNC
0.0011
0.2489      0.2408
0.1876
0.196      0.207
0.2500
1/4-24 UNS
0.0011
0.2489      0.2417
0.1978
0.205      0.215
0.2500
1/4-28 UNF
0.0010
0.2490      0.2425
0.2052
0.211      0.220
0.2500
1/4-32 UNEF
0.0010
0.2490      0.2430
0.2107
0.216      0.224
0.2500
1/4-36 UNS
0.0009
0.2491      0.2436
0.2150
0.220      0.226
0.2500
1/4-40 UNS
0.0009
0.2491      0.2440
0.2184
0.223      0.229
0.2500
1/4-48 UNS
0.0008
0.2492      0.2447
0.2236
0.227      0.232
0.2500
1/4-56 UNS
0.0008
0.2492      0.2451
0.2273
0.231      0.235
0.2500
5/16-18 UNC
0.0012
0.3113      0.3026
0.2431
0.252      0.265
0.3125
5/16-20 UN
0.0012
0.3113      0.3032
0.2500
0.258      0.270
0.3125
5/16-24-UNF
0.0011
0.3114      0.3042
0.2603
0.267      0.277
0.3125
5/16-27 UNS
0.0010
0.3115      0.3048
0.2661
0.272      0.281
0.3125
5/16-32 UNEF
0.0010
0.3115      0.3055
0.2732
0.279      0.286
0.3125
5/16-36 UNS
0.0009
0.3116      0.3061
0.2775
0.282      0.289
0.3125
5/16-40 UNS
0.0009
0.3116      0.3065
0.2809
0.285      0.291
0.3125
5/16-48 UNS
0.0008
0.3117      0.3072
0.2861
0.290      0.295
0.3125
3/8-16 UNC
0.0013
0.3737      0.3643
0.2970
0.307      0.321
0.3750
3/8-20 UN
0.0012
0.3738      0.3657
0.3125
0.321      0.332
0.3750
3/8-24 UNF
0.0011
0.3739      0.3667
0.3228
0.330      0.340
0.3750
3/8-27 UNS
0.0011
0.3739      0.3672
0.3285
0.335      0.344
0.3750
3/8-28 UN
0.0011
0.3739      0.3674
0.3301
0.336      0.345
0.3750
3/8-32 UNEF
0.0010
0.3740      0.3680
0.3357
0.341      0.349
0.3750
3/8-36 UNS
0.0010
0.3740      0.3685
0.3399
0.345      0.352
0.3750
3/8-40 UNS
0.0009
0.3741      0.3690
0.3434
0.348      0.354
0.3750

UNIFIED SCREW THREADS (CLASS 2A & 2B)

EXTERNAL (CLASS 2A)
 
INTERNAL (CLASS 2A)
Thread Size
Allowance
Major Diameter
Max          Min
Minor Dia.

Minor Diameter
Max         Min

Major Dia.   Min
0.390-27 UNS
0.0011
0.3889      0.3822
0.3435
0.350      0.359
0.3900
7/16-14 UNC
0.0014
0.4361      0.4258
0.3485
0.360      0.376
0.4375
7/16-16 UN
0.0014
0.4361      0.4267
0.3594
0.370      0.384
0.4375
7/16-18 UNS
0.0013
0.4362      0.4275
0.3680
0.377      0.390
0.4375
7/16-20 UNF
0.0013
0.4362      0.4281
0.3749
0.383      0.395
0.4375
7/16-24 UNS
0.0011
0.4364      0.4292
0.3853
0.392      0.402
0.4375
7/16-28 UNEF
0.0011
0.4364      0.4299
0.3926
0.399      0.407
0.4375
7/16-32 UN
0.0010
0.4365      0.4305
0.3982
0.404      0.411
0.4375
1/2-12 UNS
0.0016
0.4984      0.4870
0.3962
0.410      0.428
0.5000
1/2-13 UNC
0.0015
0.4985      0.4876
0.4041
0.417      0.434
0.5000
1/2-14 UNS
0.0015
0.4985      0.4882
0.4109
0.423      0.438
0.5000
1/2-16 UN
0.0014
0.4986      0.4892
0.4219
0.432      0.446
0.5000
1/2-18 UNS
0.0013
0.4987      0.4900
0.4305
0.440      0.453
0.5000
1/2-20 UNF
0.0013
0.4987      0.4906
0.4374
0.446      0.457
0.5000
1/2-24 UNS
0.0012
0.4988      0.4916
0.4477
0.455      0.465
0.5000
1/2-28 UNEF
0.0011
0.4989      0.4924
0.4551
0.461      0.470
0.5000
1/2-32 UN
0.0010
0.4990      0.4930
0.4607
0.466      0.474
0.5000
9/16-12 UNC
0.0016
0.5609      0.5495
0.4587
0.472      0.490
0.5625
9/16-14 UNS
0.0015
0.5610      0.5507
0.4734
0.485      0.501
0.5625
9/16-16 UN
0.0014
0.5611      0.5517
0.4844
0.495      0.509
0.5625
9/16-18 UNF
0.0014
0.5611      0.5524
0.4929
0.502      0.515
0.5625
9/16-20 UN
0.0013
0.5612      0.5531
0.4999
0.508      0.520
0.5625
9/16-24 UNEF
0.0012
0.5613      0.5541
0.5102
0.517      0.527
0.5625
9/16-27 UNS
0.0011
0.7485      0.7391
0.6718
0.682      0.696
0.7500
3/4-18 UNS
0.0014
0.7486      0.7399
0.6604
0.690      0.703
0.7500
3/4-20 UNEF
0.0013
0.7487      0.7406
0.6874
0.696      0.707
0.7500
3/4-24 UNS
0.0012
0.7488      0.7416
0.6977
0.705      0.715
0.7500
3/4-27 UNS
0.0012
0.7488      0.7421
0.7034
0.710      0.719
0.7500
3/4-28 UN
0.0012
0.7488      0.7423
0.7050
0.711      0.720
0.7500
3/4-32 UN
0.0011
0.7489      0.7429
0.7106
0.716      0.724
0.7500
13/16-12 UN
0.0017
0.8108      0.7994
0.7086
0.722     0.740
0.8125
13/16-16 UN
0.0015
0.8110      0.8016
0.7343
0.745     0.759
0.8125
METRIC SCREW THREADS
(all dimensions in metric except where noted)
EXTERNAL (CLASS 6G)
 
INTERNAL (CLASS6H)
Thread Size
O.D.
in Inches
Major Diameter Max          Min
Minor Diameter Max          Min
Minor Diameter Min          Max
Major Diameter Min         Max
M1.6 x 0.35
0.0629
1.581      1.496
1.202      1.075
1.221      1.321
1.600      1.736
M2 x 0.4
0.0787
1.981      1.886
1.548      1.408
1.567      1.679
2.000      2.148
M2.5 x 0.45
0.0984
2.480      2.380
1.993      1.840
2.013      2.138
2.500      2.660
M3 x 0.5
0.1181
2.980      2.874
2.439      2.272
2.459      2.599
3.000      3.172
M3.5x 0.6
0.1378
3.479      3.354
2.829      2.635
2.850      3.010
3.500      3.699
M4 x 0.7
0.1575
3.978      3.838
3.220      3.002
3.242      3.422
4.000      4.219
M5 x 0.8
0.1968
4.976      4.826
4.110      3.869
4.134      4.334
5.000      5.240
M6 x 1
0.2362
5.974      5.794
4.891      4.596
4.917      5.153
6.000      6.294
M8 x 1.25
0.3149
7.972      7.760
6.619      6.272
6.647      6.912
8.000      8.340
M8 x 1
0.3149
7.974      7.794
6.891      6.596
6.917      7.153
8.000      8.294
M10 x 1.5
0.3937
9.968      9.732
8.344      7.938
8.376      8.676
10.000      10.396
M10 x 1.25
0.3937
9.972      9.760
8.619      8.272
8.647      8.912
10.000      10.340
M10 x 0.75
0.3937
9.978      9.838
9.166      8.929
9.188      9.378
10.000      10.240
M12 x 1.75
0.4724
11.966      11.701
10.072      9.601
10.106      10.441
12.000      12.453
M12 x 1.5
0.4724
11.968      11.732
10.344      9.930
10.376      10.676
12.000      12.406
M12 x 1.25
0.4724
11.972      11.760
10.619      10.258
10.647      10.912
12.000      12.360
M12 x 1
0.4724
11.974      11.794
10.891      10.590
10.917      11.153
12.000      12.304
M14 x 2
0.5511
13.962      13.682
11.797      11.271
11.835      12.210
14.000      14.501
M14 x 1.5
0.5511
13.968      13.732
12.344      11.930
12.376      12.676
14.000      14.406
M15 x 1
0.5905
14.974      14.794
13.891      13.590
13.917      14.153
15.000      15.304
M16 x 2
0.6299
15.962      15.682
13.797      13.271
13.835      14.210
16.000      16.501
M16 x 1.5
0.6299
15.968      15.732
14.344      13.930
14.376      14.676
16.000      16.406
M17 x 1
0.6693
16.974      16.794
15.891      15.590
15.917      16.153
17.000      17.304
M18 x 1.5
0.7087
17.968      17.732
16.344      15.930
16.376      16.676
18.000      18.406
M20 x 2.5
0.7874
19.958      19.623
17.252      16.624
17.294      17.744
20.000      20.585

TAP DRILLS (UNC, UNF)
Tap Size
Drill Size
Decimal Equiv.
0-80 UNF
3/64
.0469
1-64 UNC
#53
.0595
1-72 UNF
#53
.0595
2-56 UNC
#51
.0670
2-64 UNF
#50
.0700
3-48 UNC
5/64
.0781
3-56 UNF
#46
.0810
4-40 UNC
#43
.0890
4-48 UNF
#42
.0935
5-40 UNC
#39
.0995
5-44 UNF
#37
.1040
6-32 UNC
#36
.1065
6-40 UNF
#33
.1130
8-32 UNC
#29
.1360
10-24 UNC
#25
.1495
10-32 UNF
#21
.1590
12-24 UNC
#17
.1730
12-28 UNF
#15
.1800
1/4-20 UNC
#7
.2010
1/4-28 UNF
#3
.2130
5/16-18 UNC
F
.2570
5/16-24 UNF
I
.2720
3/8-16 UNC
5/16
.3125
3/8-24 UNF
Q
.3320
7/16-14 UNC
U
.3680
1/2-13 UNC
27/64
.4219
1/2-20 UNF
29/64
.4531
9/16-12 UNC
31/64
.4844
9/16-18 UNF
33/64
.5156
5/8-11 UNC
17/32
.5312
5/8-18 UNF
37/64
.5781
3/4-10 UNC
21/32
.6562
3/4-16 UNF
11/16
.6875
7/8-9 UNC
49/64
.7656
TAP DRILLS (METRIC)
Tap Size
Drill Size
Decimal Equiv.
Pitch in Decimal
Threads per Inch
M1 x 0.25
.75
.0295
.00984
101.605
M1.1 x 0.25
.85
.0335
.00984
101.605
M1.2 x 0.25
.95
.0374
.00984
101.605
M1.4 x 0.3
1.1
.0433
.01181
84.667
M1.6 x 0.35
1.25
.0492
.01378
72.574
M1.7 x 0.35
1.3
.0512
.01378
72.574
M1.8 x 0.35
1.45
.0571
.01378
72.574
M2 x 0.4
1.6
.0630
.01575
63.500
M2.2 x 0.45
1.75
.0689
.01772
56.445
M2.5 x 0.45
2.05
.0807
.01772
56.445
M3 x 0.5
2.5
.0984
.01968
50.800
M3.5 x 0.6
2.9
.1142
.02362
42.333
M4 x 0.35
3.6
.1417
.01378
72.574
M4 x 0.5
3.5
.1378
.01968
50.800
M4 x 0.7
3.3
.1299
.02756
36.286
M4.5 x 0.75
3.7
.1457
.02953
33.867
M5 x 0.5
4.5
.1772
.01968
50.800
M5 x 0.8
4.2
.1654
.03150
31.750
M6 x 0.5
5.5
.2165
.01968
50.800
M6 x 0.75
5.25
.2067
.02953
33.867
M6 x 1
5.0
.1968
.03937
25.400
M7 x 0.75
5.25
.2067
.02953
33.867
M7 x 1
6.0
.2362
.03937
25.400
M8 x 0.5
7.5
.2953
.01968
50.800
M8 x 0.75
7.25
.2854
.02953
33.867
M8 x 1
7.0
.2756
.03937
25.400
M8 x 1.25
6.8
.2677
.04921
20.320
M9 x 1
8.0
.3150
.03937
25.400
M9 x 1.25
7.8
.3071
.04921
20.320
M10 x 0.75
9.25
.3642
.02953
33.867
M10 x 1
9.0
.3543
.03937
25.400
M10 x 1.25
8.8
.3465
.04921
20.320
M10 x 1.5
8.5
.3346
.05906
16.933

(source: Engineers Edge)

 

PIPE TAPS
TAP
SIZE
TAPER NPT
 
STRAIGHT NPS
DRILL * SIZE
DEC.
EQUIV.
Thread OD
(MAX)

Normal
Engagement

DRILL
SIZE
DEC.
EQUIV.
1/16-27
C
.242
.3125
.2611
1/4
.2500
1/8-27
Q
.332
.405
.2639
S
.3480
1/4-18
7/16
.438
.540
.4018
29/64
.4531
3/8-18
9/16
.562
.675
.4078
19/32
.5938
1/2-14
45/64
.703
.840
.5337
47/64
.7344
3/4-14
29/32
.906
1.050
.5457
15/16
.9375
1-11 1/2
1-9/64
1.141
1.315
.6828
1-3/16
1.187
* Drill sizes given permit direct tapping without reaming the hole, but only give a full thread for the first two or three threads.


Notes:

Pipe taps do not refer to any physical dimensions. The outside diameter of a pipe thread or fitting must be measured and compared to a table for size identification (see Thread OD above).

Tapered threads = 1° 47'
Truncation of roots and crests are flat
60° thread angle
Pitch is measured in threads per inch

Never use liquid sealants for NPT threads in plastic as this will cause crazing or cracking. Use teflon tape instead.

Sources:

Standard NPT Tap Drill Sizes
NPT- National Pipe Thread Taper- ANSI B1.20.1
Pipe / Pipe Thread Dimensions

 

TAP DRILLS FOR SPECIAL THREAD SIZES

To determine tap drill size for special threads, use the following formula:

TAP DRILL SIZE = DIA - (.974 / PITCH)

  EXAMPLE: 3/8-32
  .375 - (.974 / 32) = .345
  USE DRILL SIZE CLOSEST TO .345

 

 
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