O-Ring Standard

BS 4518 O-Rings — UK Standard O-Ring Manufacturer India

FITCO manufactures BS 4518 O-Rings across all five metric cross-section bands — 1.6mm, 2.4mm, 3.0mm, 5.7mm and 8.4mm — in NBR, FKM, EPDM, HNBR, Silicone and FFKM. BS 4518 is the British Standard for metric O-Rings and is not dimensionally equivalent to ISO 3601 or AS568 despite using millimetre sizing.

BS 4518 Cross-Section Series

CS	Typical ID Range	Application
1.6 mm	3.1–37.1 mm	Small bore static sealing
2.4 mm	3.6–69.6 mm	General purpose
3.0 mm	19.5–249.5 mm	Medium bore sealing
5.7 mm	44.3–499.3 mm	Large bore sealing
8.4 mm	144.1–249.1 mm	Large bore high-pressure

BS 4518 uses its own distinct ID ladder within each CS band — do not cross-reference directly to ISO 3601 or metric series without checking the dimension table. Send your BS 4518 reference number for an exact confirmation.

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Available Compounds

NBR 70/90 FKM 75/90 FFKM EPDM HNBR Silicone AFLAS Neoprene

OTHER STANDARDS WE MANUFACTURE TO

AS568 Metric ISO 3601 JIS B2401 Custom

Complete Reference

Full BS 4518 size chart — every size

All 207 standard BS 4518 O-Ring sizes across all 5 cross-section bands, with inside diameter and tolerance in millimetres.

ID (mm)	ID Tol. (±)	CS (mm)
CS 1.6 mm
3.10	0.14	1.6
4.10	0.14	1.6
5.10	0.15	1.6
6.10	0.16	1.6
7.10	0.17	1.6
8.10	0.18	1.6
9.10	0.18	1.6
10.10	0.19	1.6
11.10	0.20	1.6
12.10	0.21	1.6
13.10	0.21	1.6
14.10	0.22	1.6
15.10	0.23	1.6
16.10	0.24	1.6
17.10	0.24	1.6
18.10	0.25	1.6
19.10	0.26	1.6
20.10	0.27	1.6
21.10	0.27	1.6
22.10	0.28	1.6
25.10	0.30	1.6
27.10	0.32	1.6
29.10	0.33	1.6
32.10	0.35	1.6
35.10	0.37	1.6
37.10	0.39	1.6
CS 2.4 mm
3.60	0.14	2.4
4.60	0.15	2.4
5.60	0.16	2.4
6.60	0.16	2.4
7.60	0.17	2.4
8.60	0.18	2.4
9.60	0.19	2.4
10.60	0.19	2.4
11.60	0.20	2.4
12.60	0.21	2.4
13.60	0.22	2.4
14.60	0.22	2.4
15.60	0.23	2.4
16.60	0.24	2.4
17.60	0.25	2.4
18.60	0.25	2.4
19.60	0.26	2.4
20.60	0.27	2.4
21.60	0.28	2.4
24.60	0.30	2.4
27.60	0.32	2.4
29.60	0.33	2.4
31.60	0.35	2.4
34.60	0.37	2.4
35.60	0.38	2.4
37.60	0.39	2.4
39.60	0.41	2.4
41.60	0.42	2.4
44.60	0.44	2.4
45.60	0.45	2.4
47.60	0.46	2.4
49.60	0.48	2.4
51.60	0.49	2.4
54.60	0.51	2.4
55.60	0.52	2.4
57.60	0.53	2.4
58.60	0.54	2.4
59.60	0.55	2.4
61.60	0.56	2.4
62.60	0.57	2.4
64.60	0.58	2.4
67.60	0.60	2.4
69.60	0.62	2.4
CS 3.0 mm
19.50	0.26	3.0
21.50	0.28	3.0
22.50	0.28	3.0
24.50	0.30	3.0
25.50	0.31	3.0
26.50	0.31	3.0
27.50	0.32	3.0
29.50	0.33	3.0
31.50	0.35	3.0
32.50	0.36	3.0
34.50	0.37	3.0
35.50	0.38	3.0
36.50	0.38	3.0
37.50	0.39	3.0
39.50	0.41	3.0
41.50	0.42	3.0
42.50	0.43	3.0
44.50	0.44	3.0
49.50	0.48	3.0
54.50	0.51	3.0
55.50	0.52	3.0
57.50	0.53	3.0
59.50	0.55	3.0
62.50	0.57	3.0
64.50	0.58	3.0
69.50	0.62	3.0
74.50	0.65	3.0
79.50	0.68	3.0
84.50	0.72	3.0
89.50	0.75	3.0
94.50	0.79	3.0
99.50	0.82	3.0
104.50	0.86	3.0
109.50	0.89	3.0
114.50	0.92	3.0
119.50	0.96	3.0
124.50	0.99	3.0
129.50	1.02	3.0
134.50	1.06	3.0
139.50	1.09	3.0
144.50	1.12	3.0
149.50	1.16	3.0
154.50	1.19	3.0
159.50	1.22	3.0
164.50	1.26	3.0
169.50	1.29	3.0
174.50	1.32	3.0
179.50	1.36	3.0
184.50	1.39	3.0
189.50	1.42	3.0
194.50	1.45	3.0
199.50	1.49	3.0
209.50	1.55	3.0
219.50	1.62	3.0
229.50	1.68	3.0
239.50	1.75	3.0
244.50	1.78	3.0
249.50	1.81	3.0
CS 5.7 mm
44.30	0.44	5.7
45.30	0.45	5.7
49.30	0.48	5.7
49.50	0.48	5.7
52.30	0.50	5.7
54.30	0.51	5.7
55.30	0.52	5.7
59.30	0.55	5.7
61.30	0.56	5.7
62.30	0.57	5.7
64.30	0.58	5.7
69.30	0.61	5.7
74.30	0.65	5.7
79.30	0.68	5.7
84.30	0.72	5.7
89.30	0.75	5.7
94.30	0.79	5.7
99.30	0.82	5.7
104.30	0.85	5.7
109.30	0.89	5.7
114.30	0.92	5.7
119.30	0.96	5.7
124.30	0.99	5.7
129.30	1.02	5.7
134.30	1.06	5.7
139.30	1.09	5.7
144.30	1.12	5.7
149.30	1.16	5.7
154.30	1.19	5.7
159.30	1.22	5.7
164.30	1.26	5.7
169.30	1.29	5.7
174.30	1.32	5.7
179.30	1.35	5.7
184.30	1.39	5.7
189.30	1.42	5.7
194.30	1.45	5.7
199.30	1.49	5.7
209.30	1.55	5.7
219.30	1.62	5.7
229.30	1.68	5.7
239.30	1.75	5.7
249.30	1.81	5.7
259.30	1.88	5.7
269.30	1.94	5.7
279.30	2.01	5.7
289.30	2.07	5.7
299.30	2.14	5.7
309.30	2.20	5.7
319.30	2.26	5.7
339.30	2.39	5.7
359.30	2.52	5.7
379.30	2.65	5.7
389.30	2.71	5.7
399.30	2.77	5.7
419.30	2.90	5.7
439.30	3.03	5.7
459.30	3.15	5.7
479.30	3.28	5.7
489.30	3.34	5.7
499.30	3.40	5.7
CS 8.4 mm
144.10	1.12	8.4
149.10	1.15	8.4
154.10	1.19	8.4
159.10	1.22	8.4
164.10	1.25	8.4
169.10	1.29	8.4
174.10	1.32	8.4
179.10	1.35	8.4
184.10	1.39	8.4
189.10	1.42	8.4
194.10	1.45	8.4
199.10	1.49	8.4
204.10	1.52	8.4
209.10	1.55	8.4
219.10	1.62	8.4
229.10	1.68	8.4
234.10	1.71	8.4
239.10	1.75	8.4
249.10	1.81	8.4

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