Internal British Pipe ISO Threads (Whitworth Form) Table per. BS EN ISO 228

ISO Metric Hardware Engineering Data
Fastener and Screw / Bolt Design, Formula and Calculations

Internal Pipe Threads per. ISO 228-1, Pipe threads where pressure-tight joints are not made by the threads. These pipe threads are also known as Whitworth pipe threads.

British Pipe ISO Threads

Where:

D = Major Dia.internal thread
D1 = Minor Dia.internal thread
D2 = Pitch diameter internal thread
d = Major Dia.external thread
d1 = Minor Dia.external thread
d2 = Pitch diameter external thread
TD1 = Tolerance internal thread minor diameter
TD2 = Tolerance on the pitch diameter of the internal thread
Td = Tolerance on the major diameter of the external thread
TD2 = Tolerance on the pitch diameter of the external thread
P = Pitch
H = Height of the fundamental triangle of the thread
h = Height of the thread profile with rounded crests and roots

ISO Pipe Thread
Designation Size x Pitch
TPI
Internal ISO Pipe Thread Design Chart
Minor Dia
Pitch Dia
Major Dia
Tap Drill
Min
Max
Min
Max
Min
Max
Basic
G 1/16
G7.723x0.907
28
6.561
6.834
7.142
7.249
7.723
-
1.5875
G 1/8
G9.728x0.907
28
8.566
8.848
9.147
9.254
9.728
-
3.1750
G 1/4
G13.157x1.337
19
11.445
11.89
12.301
12.426
13.157
-
6.3500
G 3/8
G16.662x1.337
19
14.95
15.395
15.806
15.931
16.662
-
9.5250
G 1/2
G20.955x1.814
14
18.631
19.172
19.793
19.935
20.955
-
12.7000
G 5/8
G22.911x1.814
14
20.587
21.128
21.749
21.891
22.911
-
G 3/4
G26.441x1.814
14
24.117
24.658
25.279
25.421
26.441
-
15.8750
G 7/8
G30.201x1.814
14
27.877
28.418
29.039
29.181
30.201
-
22.2250
G 1
G33.249x2.309
11
30.291
30.931
31.77
31.95
33.249
-
25.4000
G 1 1/8
G37.897x2.309
11
34.939
35.579
36.418
36.598
37.897
-
28.5750
G 1 1/4
G41.91x2.309
11
38.952
39.592
40.431
40.611
41.910
-
31.7500
G 1 1/2
G47.803x2.309
11
44.845
45.485
46.324
46.504
47.803
-
38.1000
G 1 3/4
G53.746x2.309
11
50.788
51.428
52.267
52.447
53.746
-
44.4500
G 2
G59.614x2.309
11
56.656
57.296
58.135
58.315
59.614
-
50.8000
G 2 1/4
G65.71x2.309
11
62.752
63.392
64.231
64.448
65.710
-
57.1500
G 2 1/2
G75.184x2.309
11
72.226
72.866
73.705
73.922
75.184
-
G 2 3/4
G81.534x2.309
11
78.576
79.216
80.055
80.272
81.534
-
69.8500
G 3
G87.884x2.309
11
84.926
85.566
86.405
86.622
87.884
-
76.2000
G 3 1/2
G100.33x2.309
11
97.372
98.012
98.851
99.068
100.330
-
88.9000
G 4
G113.03x2.309
11
110.072
110.712
111.551
111.768
113.030
-
101.6000
G 4 1/2
G125.73x2.309
11
122.772
123.412
124.251
124.468
125.730
-
114.3000
G 5
G138.43x2.309
11
135.472
136.112
136.951
137.168
138.430
-
127.0000
G 5 1/2
G151.13x2.309
11
148.172
148.812
149.651
149.868
151.130
-
139.7000
G 6
G163.83x2.309
11
160.872
161.512
162.351
162.568
163.830
-
152.4000

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