BS 4518 O-ring standard specifications (metric)

I learned much of this information from the Precision Associates website.

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About the BS 4518 standard for O-rings

The BS 4518 standard for O-rings is produced by the British Standards Institution. The BS 4518 specification describes 203 O-rings. Each size is designated by a four digit number indicating the O-ring ID in tenths of millimeters followed by a hyphen and two digits indicating the O-ring cross-section, also in tenths of a millimeter.

In contrast to the AS 568 A inch system, the nominal and physical dimensions of metric O-rings match precisely. That is, a 1 mm O-ring will have a cross-section of 1 mm. The space that is being filled must be about 10% to 15% smaller than the cross-section of the O-ring in order for O-ring to seal properly.

Sizes within the BS 4518 standard for O-rings

Size reference code	Decimal size in millimeters		Decimal size in inches
Size reference code	Cross-section	ID	Cross-section	ID
0031-16	1.6 mm	3.1 mm	0.063 inch	0.122 inch
0041-16	1.6 mm	4.1 mm	0.063 inch	0.161 inch
0051-16	1.6 mm	5.1 mm	0.063 inch	0.201 inch
0061-16	1.6 mm	6.1 mm	0.063 inch	0.24 inch
0071-16	1.6 mm	7.1 mm	0.063 inch	0.28 inch
0081-16	1.6 mm	8.1 mm	0.063 inch	0.319 inch
0091-16	1.6 mm	9.1 mm	0.063 inch	0.358 inch
0101-16	1.6 mm	10.1 mm	0.063 inch	0.398 inch
0111-16	1.6 mm	11.1 mm	0.063 inch	0.437 inch
0121-16	1.6 mm	12.1 mm	0.063 inch	0.476 inch
0131-16	1.6 mm	13.1 mm	0.063 inch	0.516 inch
0141-16	1.6 mm	14.1 mm	0.063 inch	0.555 inch
0151-16	1.6 mm	15.1 mm	0.063 inch	0.594 inch
0161-16	1.6 mm	16.1 mm	0.063 inch	0.634 inch
0171-16	1.6 mm	17.1 mm	0.063 inch	0.673 inch
0181-16	1.6 mm	18.1 mm	0.063 inch	0.713 inch
0191-16	1.6 mm	19.1 mm	0.063 inch	0.752 inch
0221-16	1.6 mm	22.1 mm	0.063 inch	0.87 inch
0251-16	1.6 mm	25.1 mm	0.063 inch	0.988 inch
0271-16	1.6 mm	27.1 mm	0.063 inch	1.067 inch
0291-16	1.6 mm	29.1 mm	0.063 inch	1.146 inch
0321-16	1.6 mm	32.1 mm	0.063 inch	1.264 inch
0351-16	1.6 mm	35.1 mm	0.063 inch	1.382 inch
0371-16	1.6 mm	37.1 mm	0.063 inch	1.461 inch
0036-24	2.4 mm	3.6 mm	0.094 inch	0.142 inch
0046-24	2.4 mm	4.6 mm	0.094 inch	0.181 inch
0056-24	2.4 mm	5.6 mm	0.094 inch	0.22 inch
0066-24	2.4 mm	6.6 mm	0.094 inch	0.26 inch
0076-24	2.4 mm	7.6 mm	0.094 inch	0.299 inch
0086-24	2.4 mm	8.6 mm	0.094 inch	0.339 inch
0096-24	2.4 mm	9.6 mm	0.094 inch	0.378 inch
0106-24	2.4 mm	10.6 mm	0.094 inch	0.417 inch
0116-24	2.4 mm	11.6 mm	0.094 inch	0.457 inch
0126-24	2.4 mm	12.6 mm	0.094 inch	0.496 inch
0136-24	2.4 mm	13.6 mm	0.094 inch	0.535 inch
0146-24	2.4 mm	14.6 mm	0.094 inch	0.575 inch
0156-24	2.4 mm	15.6 mm	0.094 inch	0.614 inch
0166-24	2.4 mm	16.6 mm	0.094 inch	0.654 inch
0176-24	2.4 mm	17.6 mm	0.094 inch	0.693 inch
0186-24	2.4 mm	18.6 mm	0.094 inch	0.732 inch
0196-24	2.4 mm	19.6 mm	0.094 inch	0.772 inch
0206-24	2.4 mm	20.6 mm	0.094 inch	0.811 inch
0216-24	2.4 mm	21.6 mm	0.094 inch	0.85 inch
0246-24	2.4 mm	24.6 mm	0.094 inch	0.969 inch
0276-24	2.4 mm	27.6 mm	0.094 inch	1.087 inch
0296-24	2.4 mm	29.6 mm	0.094 inch	1.165 inch
0316-24	2.4 mm	31.6 mm	0.094 inch	1.244 inch
0346-24	2.4 mm	34.6 mm	0.094 inch	1.362 inch
0356-24	2.4 mm	35.6 mm	0.094 inch	1.402 inch
0376-24	2.4 mm	37.6 mm	0.094 inch	1.48 inch
0396-24	2.4 mm	39.6 mm	0.094 inch	1.559 inch
0416-24	2.4 mm	41.6 mm	0.094 inch	1.638 inch
0446-24	2.4 mm	44.6 mm	0.094 inch	1.756 inch
0456-24	2.4 mm	45.6 mm	0.094 inch	1.795 inch
0476-24	2.4 mm	47.6 mm	0.094 inch	1.874 inch
0496-24	2.4 mm	49.6 mm	0.094 inch	1.953 inch
0516-24	2.4 mm	51.6 mm	0.094 inch	2.031 inch
0546-24	2.4 mm	54.6 mm	0.094 inch	2.15 inch
0556-24	2.4 mm	55.6 mm	0.094 inch	2.189 inch
0576-24	2.4 mm	57.6 mm	0.094 inch	2.268 inch
0586-24	2.4 mm	58.6 mm	0.094 inch	2.307 inch
0596-24	2.4 mm	59.6 mm	0.094 inch	2.346 inch
0616-24	2.4 mm	61.6 mm	0.094 inch	2.425 inch
0626-24	2.4 mm	62.6 mm	0.094 inch	2.465 inch
0646-24	2.4 mm	64.6 mm	0.094 inch	2.543 inch
0676-24	2.4 mm	67.6 mm	0.094 inch	2.661 inch
0696-24	2.4 mm	69.6 mm	0.094 inch	2.74 inch
0195-30	3 mm	19.5 mm	0.118 inch	0.768 inch
0215-30	3 mm	21.5 mm	0.118 inch	0.846 inch
0225-30	3 mm	22.5 mm	0.118 inch	0.886 inch
0245-30	3 mm	24.5 mm	0.118 inch	0.965 inch
0255-30	3 mm	25.5 mm	0.118 inch	1.004 inch
0265-30	3 mm	26.5 mm	0.118 inch	1.043 inch
0275-30	3 mm	27.5 mm	0.118 inch	1.083 inch
0295-30	3 mm	29.5 mm	0.118 inch	1.161 inch
0315-30	3 mm	31.5 mm	0.118 inch	1.24 inch
0325-30	3 mm	32.5 mm	0.118 inch	1.28 inch
0345-30	3 mm	34.5 mm	0.118 inch	1.358 inch
0355-30	3 mm	35.5 mm	0.118 inch	1.398 inch
0365-30	3 mm	36.5 mm	0.118 inch	1.437 inch
0375-30	3 mm	37.5 mm	0.118 inch	1.476 inch
0395-30	3 mm	39.5 mm	0.118 inch	1.555 inch
0415-30	3 mm	41.5 mm	0.118 inch	1.634 inch
0425-30	3 mm	42.5 mm	0.118 inch	1.673 inch
0445-30	3 mm	44.5 mm	0.118 inch	1.752 inch
0495-30	3 mm	49.5 mm	0.118 inch	1.949 inch
0545-30	3 mm	54.5 mm	0.118 inch	2.146 inch
0555-30	3 mm	55.5 mm	0.118 inch	2.185 inch
0575-30	3 mm	57.5 mm	0.118 inch	2.264 inch
0595-30	3 mm	59.5 mm	0.118 inch	2.343 inch
0625-30	3 mm	62.5 mm	0.118 inch	2.461 inch
0645-30	3 mm	64.5 mm	0.118 inch	2.539 inch
0695-30	3 mm	69.5 mm	0.118 inch	2.736 inch
0745-30	3 mm	74.5 mm	0.118 inch	2.933 inch
0795-30	3 mm	79.5 mm	0.118 inch	3.13 inch
0845-30	3 mm	84.5 mm	0.118 inch	3.327 inch
0895-30	3 mm	89.5 mm	0.118 inch	3.524 inch
0945-30	3 mm	94.5 mm	0.118 inch	3.72 inch
0995-30	3 mm	99.5 mm	0.118 inch	3.917 inch
1045-30	3 mm	104.5 mm	0.118 inch	4.114 inch
1095-30	3 mm	109.5 mm	0.118 inch	4.311 inch
1145-30	3 mm	114.5 mm	0.118 inch	4.508 inch
1195-30	3 mm	119.5 mm	0.118 inch	4.705 inch
1245-30	3 mm	124.5 mm	0.118 inch	4.902 inch
1295-30	3 mm	129.5 mm	0.118 inch	5.098 inch
1345-30	3 mm	134.5 mm	0.118 inch	5.295 inch
1395-30	3 mm	139.5 mm	0.118 inch	5.492 inch
1445-30	3 mm	144.5 mm	0.118 inch	5.689 inch
1495-30	3 mm	149.5 mm	0.118 inch	5.886 inch
1545-30	3 mm	154.5 mm	0.118 inch	6.083 inch
1595-30	3 mm	159.5 mm	0.118 inch	6.28 inch
1645-30	3 mm	164.5 mm	0.118 inch	6.476 inch
1695-30	3 mm	169.5 mm	0.118 inch	6.673 inch
1745-30	3 mm	174.5 mm	0.118 inch	6.87 inch
1795-30	3 mm	179.5 mm	0.118 inch	7.067 inch
1845-30	3 mm	184.5 mm	0.118 inch	7.264 inch
1895-30	3 mm	189.5 mm	0.118 inch	7.461 inch
1945-30	3 mm	194.5 mm	0.118 inch	7.657 inch
1995-30	3 mm	199.5 mm	0.118 inch	7.854 inch
2095-30	3 mm	209.5 mm	0.118 inch	8.248 inch
2195-30	3 mm	219.5 mm	0.118 inch	8.642 inch
2295-30	3 mm	229.5 mm	0.118 inch	9.035 inch
2395-30	3 mm	239.5 mm	0.118 inch	9.429 inch
2445-30	3 mm	244.5 mm	0.118 inch	9.626 inch
2495-30	3 mm	249.5 mm	0.118 inch	9.823 inch
0443-57	5.7 mm	44.3 mm	0.224 inch	1.744 inch
0453-57	5.7 mm	45.3 mm	0.224 inch	1.783 inch
493-57	5.7 mm	49.3 mm	0.224 inch	1.941 inch
0523-57	5.7 mm	52.3 mm	0.224 inch	2.059 inch
0543-57	5.7 mm	54.3 mm	0.224 inch	2.138 inch
0553-57	5.7 mm	55.3 mm	0.224 inch	2.177 inch
0593-57	5.7 mm	59.3 mm	0.224 inch	2.335 inch
0623-57	5.7 mm	62.3 mm	0.224 inch	2.453 inch
0643-57	5.7 mm	64.3 mm	0.224 inch	2.531 inch
0693-57	5.7 mm	69.3 mm	0.224 inch	2.728 inch
0743-57	5.7 mm	74.3 mm	0.224 inch	2.925 inch
0793-57	5.7 mm	79.3 mm	0.224 inch	3.122 inch
0843-57	5.7 mm	84.3 mm	0.224 inch	3.319 inch
0893-57	5.7 mm	89.3 mm	0.224 inch	3.516 inch
0943-57	5.7 mm	94.3 mm	0.224 inch	3.713 inch
0993-57	5.7 mm	99.3 mm	0.224 inch	3.909 inch
1043-57	5.7 mm	104.3 mm	0.224 inch	4.106 inch
1093-57	5.7 mm	109.3 mm	0.224 inch	4.303 inch
1143-57	5.7 mm	114.3 mm	0.224 inch	4.5 inch
1193-57	5.7 mm	119.3 mm	0.224 inch	4.697 inch
1243-57	5.7 mm	124.3 mm	0.224 inch	4.894 inch
1293-57	5.7 mm	129.3 mm	0.224 inch	5.091 inch
1343-57	5.7 mm	134.3 mm	0.224 inch	5.287 inch
1393-57	5.7 mm	139.3 mm	0.224 inch	5.484 inch
1443-57	5.7 mm	144.3 mm	0.224 inch	5.681 inch
1493-57	5.7 mm	149.3 mm	0.224 inch	5.878 inch
1543-57	5.7 mm	154.3 mm	0.224 inch	6.075 inch
1593-57	5.7 mm	159.3 mm	0.224 inch	6.272 inch
1643-57	5.7 mm	164.3 mm	0.224 inch	6.468 inch
1693-57	5.7 mm	169.3 mm	0.224 inch	6.665 inch
1743-57	5.7 mm	174.3 mm	0.224 inch	6.862 inch
1793-57	5.7 mm	179.3 mm	0.224 inch	7.059 inch
1843-57	5.7 mm	184.3 mm	0.224 inch	7.256 inch
1893-57	5.7 mm	189.3 mm	0.224 inch	7.453 inch
1943-57	5.7 mm	194.3 mm	0.224 inch	7.65 inch
1993-57	5.7 mm	199.3 mm	0.224 inch	7.846 inch
2093-57	5.7 mm	209.3 mm	0.224 inch	8.24 inch
2193-57	5.7 mm	219.3 mm	0.224 inch	8.634 inch
2293-57	5.7 mm	229.3 mm	0.224 inch	9.028 inch
2393-57	5.7 mm	239.3 mm	0.224 inch	9.421 inch
2493-57	5.7 mm	249.3 mm	0.224 inch	9.815 inch
2593-57	5.7 mm	259.3 mm	0.224 inch	10.21 inch
2693-57	5.7 mm	269.3 mm	0.224 inch	10.6 inch
2793-57	5.7 mm	279.3 mm	0.224 inch	11 inch
2893-57	5.7 mm	289.3 mm	0.224 inch	11.39 inch
2993-57	5.7 mm	299.3 mm	0.224 inch	11.783 inch
3093-57	5.7 mm	309.3 mm	0.224 inch	12.77 inch
3193-57	5.7 mm	319.3 mm	0.224 inch	12.571 inch
3393-57	5.7 mm	339.3 mm	0.224 inch	13.358 inch
3593-57	5.7 mm	359.3 mm	0.224 inch	14.146 inch
3793-57	5.7 mm	379.3 mm	0.224 inch	14.933 inch
3893-57	5.7 mm	389.3 mm	0.224 inch	15.327 inch
3993-57	5.7 mm	399.3 mm	0.224 inch	15.72 inch
4193-57	5.7 mm	419.3 mm	0.224 inch	16.508 inch
4393-57	5.7 mm	439.3 mm	0.224 inch	17.295 inch
4593-57	5.7 mm	459.3 mm	0.224 inch	18.083 inch
4793-57	5.7 mm	479.3 mm	0.224 inch	18.87 inch
4893-57	5.7 mm	489.3 mm	0.224 inch	19.264 inch
4993-57	5.7 mm	499.3 mm	0.224 inch	19.657 inch
1441-84	8.4 mm	144.1 mm	0.331 inch	5.673 inch
1491-84	8.4 mm	149.1 mm	0.331 inch	5.87 inch
1541-84	8.4 mm	154.1 mm	0.331 inch	6.067 inch
1591-84	8.4 mm	159.1 mm	0.331 inch	6.264 inch
1641-84	8.4 mm	164.1 mm	0.331 inch	6.461 inch
1691-84	8.4 mm	169.1 mm	0.331 inch	6.657 inch
1741-84	8.4 mm	174.1 mm	0.331 inch	6.854 inch
1791-84	8.4 mm	179.1 mm	0.331 inch	7.051 inch
1841-84	8.4 mm	184.1 mm	0.331 inch	7.248 inch
1891-84	8.4 mm	189.1 mm	0.331 inch	7.445 inch
1941-84	8.4 mm	194.1 mm	0.331 inch	7.642 inch
1991-84	8.4 mm	199.1 mm	0.331 inch	7.839 inch
2041-84	8.4 mm	204.1 mm	0.331 inch	8.035 inch
2091-84	8.4 mm	209.1 mm	0.331 inch	8.232 inch
2191-84	8.4 mm	219.1 mm	0.331 inch	8.626 inch
2291-84	8.4 mm	229.1 mm	0.331 inch	9.02 inch
2341-84	8.4 mm	234.1 mm	0.331 inch	9.217 inch
2391-84	8.4 mm	239.1 mm	0.331 inch	9.413 inch
2491-84	8.4 mm	249.1 mm	0.331 inch	9.807 inch