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ASME/ANSI B16.5 - Flanges and Bolt Dimensions Class 150 to 2500

Diameters and bolt circles for standard ASME B16.5 flanges - 1/4 to 24 inches - Class 150 to 2500

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Flange dimensions are determined by the pipe size and the pressure class required for the application. Flanges are standardized according publications from organizations like ASME, MSS, API and others.

ASME/ANSI B16.5 provides

  • weld neck
  • slip-on
  • socket weld
  • threaded
  • lap joint
  • blind

flange dimensions for pipes ranging 1/2" to 24" - in classes ranging 150 to 2500.

Nominal Pipe Size
NPS
(inches)
Class 150
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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
  • 1 inch = 25.4 mm
Nominal Pipe Size
NPS
(inches)
Class 300
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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)
Class 400
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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)
Class 600
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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)
Class 900
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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)
Class 1500
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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)
Class 2500
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt 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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