Spiral Wound Gasket Dimensions

Spiral wound gaskets are the most widely used semi-metallic gaskets in the oil and gas industry for raised face (RF) flanges. Their dimensions are standardized by ASME B16.20, which specifies the inner diameter, outer diameter, inner ring ID, outer (centering) ring OD, and thickness for each pipe size and pressure class. The following tables provide spiral wound gasket dimensions for Class 150, Class 300, and Class 600 raised face flanges.

Spiral Wound Gasket Dimensions - Class 150 RF

NPS	Gasket ID (inch)	Gasket OD (inch)	Inner Ring ID (inch)	Outer Ring OD (inch)	Thickness (inch)
1/2	0.88	1.88	0.63	2.12	0.175
3/4	1.09	2.12	0.81	2.50	0.175
1	1.38	2.50	1.06	2.88	0.175
1-1/4	1.72	2.88	1.38	3.25	0.175
1-1/2	1.97	3.25	1.63	3.62	0.175
2	2.50	3.88	2.06	4.25	0.175
2-1/2	2.94	4.62	2.50	5.00	0.175
3	3.56	5.12	3.06	5.50	0.175
3-1/2	4.06	5.75	3.56	6.12	0.175
4	4.63	5.88	4.06	6.50	0.175
5	5.69	7.12	5.06	7.50	0.175
6	6.75	8.25	6.06	8.75	0.175
8	8.38	10.25	7.81	10.75	0.175
10	10.56	12.62	9.94	13.00	0.175
12	12.12	14.25	11.56	15.00	0.175
14	13.25	16.25	12.56	16.75	0.175
16	15.25	18.25	14.56	18.75	0.175
18	17.25	20.50	16.56	21.00	0.175
20	19.25	22.50	18.56	23.00	0.175
24	23.25	26.62	22.56	27.25	0.175

Spiral Wound Gasket Dimensions - Class 300 RF

NPS	Gasket ID (inch)	Gasket OD (inch)	Inner Ring ID (inch)	Outer Ring OD (inch)	Thickness (inch)
1/2	0.88	1.88	0.63	2.12	0.175
3/4	1.09	2.25	0.81	2.62	0.175
1	1.38	2.62	1.06	3.00	0.175
1-1/4	1.72	3.00	1.38	3.38	0.175
1-1/2	1.97	3.38	1.63	3.75	0.175
2	2.50	4.12	2.06	4.50	0.175
2-1/2	2.94	4.88	2.50	5.25	0.175
3	3.56	5.38	3.06	5.75	0.175
3-1/2	4.06	5.88	3.56	6.25	0.175
4	4.63	6.50	4.06	7.00	0.175
5	5.69	7.50	5.06	7.88	0.175
6	6.75	8.75	6.06	9.25	0.175
8	8.38	10.75	7.81	11.25	0.175
10	10.56	13.00	9.94	13.50	0.175
12	12.12	15.00	11.56	15.50	0.175
14	13.25	16.75	12.56	17.25	0.175
16	15.25	18.75	14.56	19.25	0.175
18	17.25	21.00	16.56	21.50	0.175
20	19.25	23.00	18.56	23.50	0.175
24	23.25	27.25	22.56	27.75	0.175

Spiral Wound Gasket Dimensions - Class 600 RF

NPS	Gasket ID (inch)	Gasket OD (inch)	Inner Ring ID (inch)	Outer Ring OD (inch)	Thickness (inch)
1/2	0.88	1.88	0.63	2.12	0.175
3/4	1.09	2.25	0.81	2.62	0.175
1	1.38	2.62	1.06	3.00	0.175
1-1/4	1.72	3.00	1.38	3.38	0.175
1-1/2	1.97	3.38	1.63	3.75	0.175
2	2.50	4.12	2.06	4.50	0.175
2-1/2	2.94	4.88	2.50	5.25	0.175
3	3.56	5.38	3.06	5.75	0.175
3-1/2	4.06	5.88	3.56	6.25	0.175
4	4.63	6.50	4.06	7.00	0.175
5	5.69	7.50	5.06	7.88	0.175
6	6.75	8.75	6.06	9.25	0.175
8	8.38	10.75	7.81	11.25	0.175
10	10.56	13.00	9.94	13.50	0.175
12	12.12	15.00	11.56	15.50	0.175
14	13.25	16.75	12.56	17.25	0.175
16	15.25	18.75	14.56	19.25	0.175
18	17.25	21.00	16.56	21.50	0.175
20	19.25	23.00	18.56	23.50	0.175
24	23.25	27.25	22.56	27.75	0.175

Notes

• All dimensions are per ASME B16.20, which covers metallic gaskets for pipe flanges (ring-joint, spiral-wound, and jacketed types).
• The standard thickness for spiral wound gaskets is 0.175 inches (4.5 mm), which includes the compressed sealing element. The uncompressed thickness before installation is typically 0.185 to 0.195 inches.
• Spiral wound gaskets for RF flanges consist of alternating plies of metal strip and soft filler material, wound into a V-shaped cross-section. The most common material combinations are 304SS/graphite filler, 316SS/graphite filler, and 316SS/PTFE filler. The 304SS/graphite combination is suitable for most general service applications, while 316SS/graphite is preferred for corrosive environments.
• The inner ring (solid metal) prevents inward buckling of the winding under bolt load and protects against erosion from the process fluid. It is required for applications involving vacuum service, high-pressure steam, or thermally cycling conditions.
• The outer centering ring (typically carbon steel or 304SS) centers the gasket on the flange bolt circle and acts as a compression stop to prevent over-compression. Its OD is designed to fit within the bolt holes of the corresponding flange size and class.
• For Class 900 and higher pressure classes, consult ASME B16.20 directly, as some gasket dimensions differ from Class 600.
• Gasket material selection should consider the process fluid, temperature range, and pressure. Graphite-filled gaskets are suitable for temperatures up to approximately 450 degrees C (850 degrees F), while PTFE-filled gaskets are limited to approximately 260 degrees C (500 degrees F).