ANSI B16.5 Forged Flanges

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

Nominal Pipe Size
NPS
(inches)
Diameter of
Flange
(inches)
No.
of
Bolts
Diameter of
Bolts
(inches)
Diameter of
Bolt Holes
(inches)
Bolt
Circle
(inches)
ANSI Class 150
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
ANSI Class 300
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
ANSI Class 400
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
ANSI Class 600
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
ANSI Class 900
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
ANSI Class 1500
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
ANSI Class 2500
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