Cast Iron Flanges - ASME/ANSI Class 250

ASME/ANSI B16.1 Cast Iron Pipe Flanges and Flanged Fittings - Class 250 Flanges - outside and inside diameters, bolt circles, numbers and diameters of bolts.

Pipe Size (inches)	Outside Diameter (inches)	Number of Bolt Holes	Bolt Hole Diameter (inches)	Bolt Circle (inches)
1	4-7/8	4	3/4	3-1/2
1-1/4	5-1/4	4	3/4	3-7/8
1-1/2	6-1/8	4	7/8	4-1/2
2	6-1/2	8	3/4	5
2-1/2	7-1/2	8	7/8	5-7/8
3	8-1/4	8	7/8	6-5/8
3-1/2	9	8	7/8	7-1/4
4	10	8	7/8	7-7/8
5	11	8	7/8	9-1/4
6	12-1/2	12	7/8	10-5/8
8	15	12	1	13
10	17-1/2	16	1-1/8	15-1/4
12	20-1/2	16	1-1/4	17-3/4
14	23	20	1-1/4	20-1/4
16	25-1/2	20	1-3/8	22-1/2
18	28	24	1-3/8	24-3/4
20	30-1/2	24	1-3/8	27
24	36	24	1-5/8	32
30	43	28	2	39-1/4
36	50	32	2-1/4	46
42	57	36	2-1/4	52-3/4
48	65	40	2-1/4	60-3/4