ASME B16.5 : Complete Guide to Weld Neck Flange Dimensions

ASME B16.5, a crucial standard published by the American Society of Mechanical Engineers, covers the dimensions, pressure-temperature ratings, materials, tolerances, marking, and testing of pipe flanges and flanged fittings for sizes from NPS 1/2″ to 24″. Within this comprehensive standard, weld neck flange is a common and critical component.

Similarly, when considering other types of flanges under ASME B16.5, understanding their specific dimensions is just as important. This article, for instance, focuses on introducing the sizes of blind flanges across various pressure classes, including 150#, 300#, 400#, 600#, 900#, 1500#, and 2500#.

Weld Neck Flanges are a specific type of flange covered by ASME B16.5. They are characterized by a long, tapered hub that is butt-welded to the pipe. This tapered hub provides a smooth transition from the pipe to the flange, distributing stress more evenly and making them ideal for high-pressure, high-temperature, and critical applications.

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ZIZI specializes in producing and exporting various types of weld neck flanges, specifically including flat face weld neck flanges (FF), raised face weld neck flanges (RF), and ring joint weld neck flanges (RTJ). As a professional weld neck flanges manufacturer, we have an advanced steel flange production line that integrates forging, rolling, and precision machining processes.

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WN Class 150 lb

Weld Neck Flange Dimensions Class 150 (ASME B16.5 ) in Millimeters

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	88.90	15.70	11.20	47.80	21.30	30.20	35.00	4	15.70	60.45	0.48
3/4	26.70	98.60	20.80	12.70	52.30	26.70	38.10	42.90	4	15.70	69.85	0.71
1	33.40	108.0	26.70	14.20	55.60	33.50	49.30	50.80	4	15.70	79.25	1.01
11/4	42.20	117.3	35.10	15.70	57.15	42.20	58.70	63.50	4	15.70	88.90	1.33
11/2	48.30	127.0	40.90	17.50	62.00	48.30	65.00	73.15	4	15.70	98.60	1.72
2	60.30	152.4	52.60	19.10	63.50	60.45	77.70	91.90	4	19.10	120.7	2.58
21/2	73.00	177.8	62.70	22.40	69.85	73. 15	90.4	104.6	4	19.10	139.7	4.11
3	88.90	190.5	78.00	23.90	69.85	88.90	108.0	127.0	4	19.10	152.4	4.92
31/2	101.6	215.9	90.20	23.90	71.40	101.6	122.2	139.7	8	19.10	177.8	6.08
4	114.3	228.6	102.40	23.90	76.20	114.3	134.9	157.2	8	19.10	190.5	6.84
5	141.3	254.0	128.3	23.90	88.90	141.2	163.6	185.7	8	22.40	215.9	8.56
6	168.3	279.4	154.2	25.40	88.90	168.4	192.0	215.9	8	22.40	241.3	10.6
8	219.1	342.9	202.7	28.40	101.6	219.2	246.1	269.7	8	22.40	298.5	17.6
10	273.0	406.4	254.5	30.20	101.6	273.0	304.8	323.8	12	25.40	362.0	24.0
12	323.8	482.6	304.8	31.75	114.3	323.8	365.3	381.0	12	25.40	431.8	36.5
14	355.6	533.4	To be specified by the Purchaser	35.10	127.0	355.6	400.1	412.7	12	28.40	476.3	48.4
16	406.4	596.9		36.60	127.0	406.4	475.2	469.9	16	28.40	539.8	60.6
18	457.2	635.0		39.60	139.7	457.2	505.0	533.4	16	31.75	577.9	68.3
20	508.0	698.5		42.90	144.5	508.0	558.8	584.2	20	31.75	635.0	84.5
24	609.6	812.8		47.80	152.4	609.6	663.4	692.1	20	35.10	749.3	115

WN Class 300 lb

Weld Neck Flange Dimensions Class 300 (ASME B16.5 ) in Millimeters.

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	95.20	15.70	14.20	52.30	21.30	38.10	35.00	4	15.70	66.55	0.75
3/4	26.70	117.3	20.80	15.70	57.15	26.70	47.70	42.90	4	19.00	82.50	1.26
1	33.40	123.9	26.70	17.50	62.00	33.50	53.80	50.80	4	19.00	88.90	1.52
1 1/4	42.20	133.3	35.10	19.00	65.00	42.20	63.50	63.50	4	19.00	98.50	2.03
1 1/2	48.30	155.4	40.90	20.60	68.30	48.30	69.85	73. 15	4	22.30	114.3	2.89
2	60.30	165. 1	52.60	22.30	69.85	60.45	84.00	91.90	8	19.00	127.0	3.4
2 1/2	73.00	190.5	62.70	25.40	76.20	73.15	100.0	104.6	8	22.30	149.3	5.17
3	88.90	209.5	78.00	28.40	79.25	88.90	117.3	127.0	8	22.30	168.1	6.93
3 1/2	101.6	228.6	90.20	30.20	81.00	101.6	133.3	139.7	8	22.30	184.1	8.67
4	114.3	254.0	102.4	31.70	85.80	114.3	146.0	157.2	8	22.30	200.1	11.2
5	141.3	279.4	128.3	35.00	98.50	141.2	177.8	185.7	8	22.30	234.9	15.1
6	168.3	317.5	154.2	36.50	98.50	168.4	206.2	215.9	12	22.30	269.7	19.1
8	219.1	381.0	202.7	41.10	111.2	219.2	260.3	269.7	12	25.40	330.2	29.9
10	273.0	444.5	254.5	47.70	117.3	273.0	320.5	323.8	16	28.40	387.3	42.7
12	323.8	520.7	304.8	50.80	130.0	323.8	374.6	381.0	16	31.70	450.8	61.8
14	355.6	584.2	To be specified by the Purchaser	53.80	142.7	355.6	425.4	412.7	20	31.70	514.3	85.8
16	406.4	647.7		57.15	146.0	406.4	482.6	469.9	20	35.00	571.5	106
18	457.2	711.2		60.45	158.7	457.2	533.4	533.4	24	35.00	628.6	131
20	508.0	774.7		63.50	162.0	508.0	587.2	584.2	24	35.00	685.8	158
24	609.6	914.4		69.85	168.1	609.6	701.5	692.1	24	41.10	812.8	230

WN Class 400 lb

Weld Neck Flange Dimensions Class 400 (ASME B16.5 ) in Millimeters

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	95.30	To be specified by the Purchaser	14.20	52.30	21.30	38.10	35.00	4	15.70	66.55	0.87
3/4	26.70	117.3		15.70	57.15	26.70	47.80	42.90	4	19.10	82.60	1.45
1	33.40	124.0		17.50	62.00	33.50	53.80	50.80	4	19.10	88.90	1.76
11/4	42.20	133.4		20.60	66.55	42.20	63.50	63.50	4	19.10	98.60	2.49
11/2	48.30	155.4		22.40	69.85	48.30	69.85	73.15	4	22.40	114.3	3.49
2	60.30	165.1		25.40	73.15	60.45	84.10	91.90	8	19.10	127.0	4.36
21/2	73.00	190.5		28.40	79.25	73.15	100.1	104.6	8	22.40	149.4	6.43
3	88.90	209.6		31.75	82.60	88.90	117.3	127.0	8	22.40	168. 1	8.53
31/2	101.6	228.6		35.10	85.90	101.6	133.4	139.7	8	25.40	84.2	10.7
4	114.3	254.0		35.10	88.90	114.3	146.1	157.2	8	25.40	200.2	12.8
5	141.3	279.4		38.10	101.6	141.2	177.8	185.7	8	25.40	235.0	16.9
6	168.3	317.5		41.10	103.1	168.4	206.2	215.9	12	25.40	269.7	22.0
8	219. 1	381.0		47.80	117.3	219.2	260.4	269.7	12	28.40	330.2	34.7
10	273.0	444.5		53.80	124.0	273.0	320.5	323.8	16	31.75	387.4	48.5
12	323.8	520.7		57.15	5.380 136.7	323.8	374.7	381.0	16	35.10	450.9	69.6
14	355.6	584.2		60.45	149.4	355.6	425.5	412.7	20	35.10	514.4	95.5
16	406.4	647.7		63.50	152.4	406.4	482.6	469.9	20	38.10	571.5	118
18	457.2	711.2		66.55	165.1	457.2	533.4	533.4	24	38.10	628.7	145
20	508.0	774.7		69.85	168.1	508.0	587.2	584.2	24	41.10	685.8	173
24	609.6	914.4		76.20	174.8	609.6	701.5	692.1	24	47.80	812.8	249

WN Class 600 lb

Weld Neck Flange Dimensions Class 600 (ASME B16.5 ) in Millimeters.

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	95.30	To be specified by the Purchaser	14.20	52.30	21.30	38.10	35.00	4	15.70	66.55	0.87
3/4	26.70	117.3		15.70	57.15	26.70	47.80	42.90	4	19.10	82.60	1.45
1	33.40	124.0		17.50	62.00	33.50	53.80	50.80	4	19.10	88.90	1.76
11/4	42.20	133.4		20.60	66.55	42.20	63.50	63.50	4	19.10	98.60	2.49
11/2	48.30	155.4		22.40	69.85	48.30	69.85	73. 15	4	22.40	114.3	3.49
2	60.30	165. 1		25.40	73.15	60.45	84.10	91.90	8	19.10	127.0	4.36
21/2	73.00	190.5		28.40	79.25	73.15	100.1	104.6	8	22.40	149.4	6.43
3	88.90	209.6		31.75	82.60	88.90	117.3	127.0	8	22.40	168.1	8.53
31/2	101.6	228.6		35.10	85.90	101.6	133.4	139.7	8	25.40	184.2	10.7
4	114.3	273. 1		38.10	101.6	114.3	152.4	157.2	8	25.40	215.9	17.4
5	141.3	330.2		44.50	114.3	141.2	189.0	185.7	8	28.40	266.7	29.2
6	168.3	355.6		47.80	117.3	168.4	222.3	215.9	12	28.40	292.1	34.9
8	219.1	419. 1		55.60	133.4	219.2	273.1	269.7	12	31.75	349.3	53.9
10	273.0	508.0		63.50	152.4	273.0	342.9	323.8	16	35.10	431.8	86.5
12	323.8	558.8		66.55	155.4	323.8	400.1	381.0	20	35.10	489.0	103
14	355.6	603.3		69.85	165.1	355.6	431.8	412.7	20	38.10	527.1	122
16	406.4	685.8		76.20	177.8	406.4	495.3	469.9	20	41.10	603.3	170
18	457.2	743.0		82.60	184.2	457.2	546.1	533.4	20	44.50	654.1	204
20	508.0	812.8		88.90	190.5	508.0	609.6	584.2	24	44.50	723.9	254
24	609.6	939.8		101.6	203.2	609.6	717.6	692.1	24	50.80	838.2	358

WN Class 900 lb

Weld Neck Flange Dimensions Class 900 (ASME B16.5 ) in Millimeters.

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	120.6	To be specified by the Purchaser	22.30	60.45	21.30	38.10	35.00	4	22.30	82.50	1.87
3/4	26.70	130.0		25.40	69.85	26.70	44.00	42.90	4	22.30	88.90	2.56
1	33.40	149.3		28.40	73.15	33.50	52.30	50.80	4	25.40	101.6	3.74
11/4	42.20	158.7		28.40	73.15	42.20	63.50	63.50	4	25.40	111.2	4.33
11/2	48.30	177.8		31.70	82.50	48.30	69.85	73.15	4	28.40	123.9	5.94
2	60.30	215.9		38.10	101.6	60.45	104.6	91.90	8	25.40	165.1	10.8
21/2	73.00	244.3		41.10	104.6	73.15	123.9	104.6	8	28.40	190.5	15.0
3	88.90	241.3		38.10	101.6	88.90	127.0	127.0	8	25.40	190.5	13.7
4	114.3	292.1		44.40	114.3	114.3	158.7	157.2	8	31.70	234.9	22.5
5	141.3	349.2		50.80	127.0	141.2	190.5	185.7	8	35.00	279.4	37.4
6	168.3	381.0		55.60	139.7	168.4	234.9	215.9	12	31.70	317.5	47.7
8	219. 1	469.9		63.50	162.0	219.2	298.4	269.7	12	38.10	393.7	81.3
10	273.0	546.1		69.85	184. 1	273.0	368.3	323.8	16	38.10	469.9	119
12	323.8	609.6		79.25	200. 1	323.8	419.1	381.0	20	38.10	533.4	157
14	355.6	641.3		85.80	212.8	355.6	450.8	412.7	20	41.10	558.8	180
16	406.4	704.8		88.90	215.9	406.4	508.0	469.9	20	44.40	615.9	217
18	457.2	787.4		101.6	228.6	457.2	565.1	533.4	20	50.80	685.8	292
20	508.0	857.2		107.9	247.6	508.0	622.3	584.2	20	53.80	749.3	362
24	609.6	1041.4		139.7	292. 1	609.6	749.3	692.1	20	66.55	901.7	665

WN Class 1500 lb

Weld Neck Flange Dimensions Class 1500 (ASME B16.5 ) in Millimeters.

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	120.6	To be specified by the Purchaser	22.30	60.45	21.30	38.10	35.00	4	22.30	82.50	1.87
3/4	26.70	130.0		25.40	69.85	26.70	44.00	42.90	4	22.30	88.90	2.56
1	33.40	149.3		28.40	73.15	33.50	52.30	50.80	4	25.40	101.6	3.74
11/4	42.20	158.7		28.40	73.15	42.20	63.50	63.50	4	25.40	111.2	4.33
11/2	48.30	177.8		31.70	82.50	48.30	69.85	73. 15	4	28.40	123.9	5.94
2	60.30	215.9		38.10	101.6	60.45	104.6	91.90	8	25.40	165.1	10.8
21/2	73.00	244.3		41.10	104.6	73.15	123.9	104.6	8	28.40	190.5	15.0
3	88.90	266.7		47.70	177.3	88.9	133.3	127.0	8	31.70	203.2	19.9
4	114.3	311.1		53.80	123.9	114.3	162.0	157.2	8	35.00	241.3	29.9
5	141.3	374.6		73.15	155.4	141.2	196.8	185.7	8	41.10	292.1	55.4
6	168.3	393.7		82.50	171.4	168.4	228.6	215.9	12	38.10	317.5	68.4
8	219.1	482.6		91.90	212.8	219.2	292.1	269.7	12	44.40	393.7	117
10	273.0	584.2		107.9	254.0	273.0	368.3	323.8	12	50.80	482.6	194
12	323.8	673. 1		123.9	282.4	323.8	450.8	381.0	16	53.80	571.5	288
14	355.6	749.3		133.3	298.4	355.6	495.3	412.7	16	60.45	635.0	380
16	406.4	825.5		146.0	311. 1	406.4	552.4	469.9	16	66.55	704.8	485
18	457.2	914.4		162.0	327.1	457.2	596.9	533.4	16	73.15	774.7	644
20	508.0	984.2		177.8	355.6	508.0	641.3	584.2	16	79.25	831.8	775
24	609.6	1168.4		203.2	406.4	609.6	762.0	692.1	16	91.90	990.6	1232

WN Class 2500 lb

Weld Neck Flange Dimensions Class 2500 (ASME B16.5 ) in Millimeters.

Nominal Pipe Size		A	B	C	D	E	F	G	H	I	J	Weight
inch	mm	mm	mm	mm	mm	mm	mm	mm	Holes	mm	mm	kg / piece
1/2	21.30	133.4	To be specified by the Purchaser	30.20	73. 15	21.30	42.90	35.00	4	22.40	88.90	3.12
3/4	26.70	139.7		31.75	79.25	26.70	50.80	42.90	4	22.40	95.30	3.70
1	33.40	158.8		35.10	88.90	33.50	57.15	50.80	4	25.40	108.0	5.24
11/4	42.20	184.2		38.10	95.30	42.20	73.15	63.50	4	28.40	130.0	7.74
11/2	48.30	203.2		44.50	111.3	48.30	79.25	73.15	4	31.75	146. 1	10.9
2	60.30	235.0		50.80	127.0	60.45	95.30	91.90	8	28.40	171.5	16.2
21/2	73.00	266.7		57.15	142.7	73.15	114.3	104.6	8	31.75	196.9	23.7
3	88.90	304.8		66.55	168.1	88.90	133.4	127.0	8	35.10	228.6	36.2
4	114.3	355.6		76.20	190.5	114.3	165.1	157.2	8	41.10	273. 1	55.3
5	141.3	419.1		91.90	228.6	141.2	203.2	185.7	8	47.80	323.9	92.5
6	168.3	482.6		108	273.1	168.4	235.0	215.9	8	53.80	368.3	143
8	219.1	552.5		127.0	317.5	219.2	304.8	269.7	12	53.80	438.2	215
10	273.0	673.1		165.1	419.1	273.0	374.7	323.8	12	66.55	539.8	406
12	323.8	762.0		184.2	463.6	323.8	441.5	381.0	12	73.15	619.3	572

June 5, 2025