ASME sets the standards for flanges and bolt dimensions through the ANSI accredited ASME Standard B 16.5 ensuring all gasket and flange fittings are consistent and fit for purpose allowing a high-quality seal.
Below are the standard measurements for flanges and their relevant bolts and holes size – a very useful tool for any onsite machinist.
Flange and bolt dimensions – Class 150 to 2500
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/4
3-3/8
4
1/2
0.62
2-1/4
1/2
3-1/2
4
1/2
0.62
2-3/8
3/4
3-7/8
4
1/2
0.62
2-3/4
1
4-1/4
4
1/2
0.62
3-1/8
1-1/4
4-5/8
4
1/2
0.62
3-1/2
1-1/2
5
4
1/2
0.62
3-7/8
2
6
4
5/8
0.75
4-3/4
2-1/2
7
4
5/8
0.75
5-1/2
3
7-1/2
4
5/8
0.75
6
3-1/2
8-1/2
8
5/8
0.75
7
4
9
8
5/8
0.75
7-1/2
5
10
8
3/4
0.88
8-1/2
6
11
8
3/4
0.88
9-1/2
8
13-1/2
8
3/4
0.88
11-3/4
10
16
12
7/8
1
14-1/4
12
19
12
7/8
1
17
14
21
12
1
1.12
18-3/4
16
23-1/2
16
1
1.12
21-1/4
18
25
16
1-1/8
1.25
22-3/4
20
27-1/2
20
1-1/8
1.25
25
24
32
20
1-1/4
1.38
29-1/2
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/4
3-3/8
4
1/2
0.62
2-1/4
1/2
3-3/4
4
1/2
0.62
2-5/8
3/4
4-5/8
4
5/8
0.75
3-1/4
1
4-7/8
4
5/8
0.75
3-1/2
1-1/4
5-1/4
4
5/8
0.75
3-7/8
1-1/2
6-1/8
4
3/4
0.88
4-1/2
2
6-1/2
8
5/8
0.75
5
2-1/2
7-1/2
8
3/4
0.88
5-7/8
3
8-1/4
8
3/4
0.88
6-5/8
3-1/2
9
8
3/4
0.88
7-1/4
4
10
8
3/4
0.88
7-7/8
5
11
8
3/4
0.88
9-1/4
6
12-1/2
12
3/4
0.88
10-5/8
8
15
12
7/8
1
13
10
17-1/2
16
1
1.12
15-1/4
12
20-1/2
16
1-1/8
1.25
17-3/4
14
23
20
1-1/8
1.25
20-1/4
16
25-1/2
20
1-1/4
1.38
22-1/2
18
28
24
1-1/4
1.38
24-3/4
20
30-1/2
24
1-1/4
1.38
27
24
36
24
1-1/2
1.62
32
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/4
3-3/8
4
1/2
0.62
2-1/4
1/2
3-3/4
4
1/2
0.62
2-5/8
3/4
4-5/8
4
5/8
0.75
3-1/4
1
4-7/8
4
5/8
0.75
3-1/2
1-1/4
5-1/4
4
5/8
0.75
3-7/8
1-1/2
6-1/8
4
3/4
0.88
4-1/2
2
6-1/2
8
5/8
0.75
5
2-1/2
7-1/2
8
3/4
0.88
5-7/8
3
8-1/4
8
3/4
0.88
6-5/8
3-1/2
9
8
7/8
1
7-1/4
4
10
8
7/8
1
7-7/8
5
11
8
7/8
1
9-1/4
6
12-1/2
12
7/8
1
10-5/8
8
15
12
1
1.12
13
10
17-1/2
16
1-1/8
1.25
15-1/4
12
20-1/2
16
1-1/4
1.38
17-3/4
14
23
20
1-1/4
1.38
20-1/4
16
25-1/2
20
1-3/8
1.5
22-1/2
18
28
24
1-3/8
1.5
24-3/4
20
30-1/2
24
1-1/2
1.62
27
24
36
24
1-3/4
1.88
32
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/4
3-3/8
4
1/2
0.62
2-1/4
1/2
3-3/4
4
1/2
0.62
2-5/8
3/4
4-5/8
4
5/8
0.75
3-1/4
1
4-7/8
4
5/8
0.75
3-1/2
1-1/4
5-1/4
4
5/8
0.75
3-7/8
1-1/2
6-1/8
4
3/4
0.88
4-1/2
2
6-1/2
8
5/8
0.75
5
2-1/2
7-1/2
8
3/4
0.88
5-7/8
3
8-1/4
8
3/4
0.88
6-5/8
3-1/2
9
8
7/8
1
7-1/4
4
10-3/4
8
7/8
1
8-1/2
5
13
8
1
1.12
10-1/2
6
14
12
1
1.12
11-1/2
8
16-1/2
12
1-1/8
1.25
13-3/4
10
20
16
1-1/4
1.38
17
12
22
20
1-1/4
1.38
19-1/4
14
23-3/4
20
1-3/8
1.5
20-3/4
16
27
20
1-1/2
1.62
23-3/4
18
29-1/4
20
1-5/8
1.75
25-3/4
20
32
24
1-5/8
1.75
28-1/2
24
37
24
1-7/8
2
33
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/2
4-3/4
4
3/4
0.88
3-1/4
3/4
5-1/8
4
3/4
0.88
3-1/2
1
5-7/8
4
7/8
1
4
1-1/4
6-1/4
4
7/8
1
4-3/8
1-1/2
7
4
1
1.12
4-7/8
2
8-1/2
8
7/8
1
6-1/2
2-1/2
9-5/8
8
1
1.12
7-1/2
3
9-1/2
8
7/8
1
7-1/2
4
11-1/2
8
1-1/8
1.25
9-1/4
5
13-3/4
8
1-1/4
1.38
11
6
15
12
1-1/8
1.25
12-1/2
8
18-1/2
12
1-3/8
1.5
15-1/2
10
21-1/2
16
1-3/8
1.5
18-1/2
12
24
20
1-3/8
1.5
21
14
25-1/4
20
1-1/2
1.62
22
16
27-3/4
20
1-5/8
1.75
24-1/2
18
31
20
1-7/8
2
27
20
33-3/4
20
2
2.12
29-1/2
24
41
20
2-1/2
2.62
35-1/2
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/2
4-3/4
4
3/4
0.88
3-1/4
3/4
5-1/8
4
3/4
0.88
3-1/2
1
5-7/8
4
7/8
1
4
1-1/4
6-1/4
4
7/8
1
4-3/8
1-1/2
7
4
1
1.12
4-7/8
2
8-1/2
8
7/8
1
6-1/2
2-1/2
9-5/8
8
1
1.12
7-1/2
3
10-1/2
8
1-1/8
1.25
8
4
12-1/4
8
1-1/4
1.38
9-1/2
5
14-3/4
8
1-1/2
1.62
11-1/2
6
15-1/2
12
1-3/8
1.5
12-1/2
8
19
12
1-5/8
1.75
15-1/2
10
23
12
1-7/8
2
19
12
26-1/2
16
2
2.12
22-1/2
14
29-1/2
16
2-1/4
2.38
25
16
32-1/2
16
2-1/2
2.62
27-3/4
18
36
16
2-3/4
2.88
30-1/2
20
38-3/4
16
3
3.12
32-3/4
24
46
16
3-1/2
3.62
39
Nominal Pipe Size NPS (inches)
Diameter of Flange (inches)
No. of Bolts
Diameter of Bolts(inches)
Diameter ofBolt Holes (inches)
Bolt Circle(inches)
1/2
5-1/4
4
3/4
0.88
3-1/2
3/4
5-1/2
4
3/4
0.88
3-3/4
1
6-1/4
4
7/8
1
4-1/4
1-1/4
7-1/4
4
1
1.12
5-1/8
1-1/2
8
4
1-1/8
1.25
5-3/4
2
9-1/4
8
1
1.12
6-3/4
2-1/2
10-1/2
8
1-1/8
1.25
7-3/4
3
12
8
1-1/4
1.38
9
4
14
8
1-1/2
1.62
10-3/4
5
16-1/2
8
1-3/4
1.88
12-3/4
6
19
8
2
2.12
14-1/2
8
21-3/4
12
2
2.12
17-1/4
10
26-1/2
12
2-1/2
2.62
21-1/4
12
30
12
2-3/4
2.88
24-3/8
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Flange maintenance Tools
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