This is an o-ring commonly used to seal coolant pipes together. The OD is 14.5mm and the ring thickness is 2.5mm. Sometimes a coolant leak can be from a small seal like this and a new hose or connector is not required.
This part is manufactured by an aftermarket supplier of European auto parts, including many gaskets and seals. While not carrying OEM status, this part follows the design of the original very closely and uses similar materials. An aftermarket part may even have the same TUV approval as its OEM counterpart. The brand may even be OEM to another manufacturer besides BMW. This aftermarket brand has a two year warranty - the same as Genuine BMW and OEM brands.
BMW Fitments:
1 Series
E82 / E88 (08-13) > 128i
E82 / E88 (08-13) > 135i N54 (08-10)
E82 / E88 (08-13) > 135i N55 (11-13)
E82 / E88 (08-13) > 135is N55 (11-13)
3 Series
E46 (99-05) > 320i
E46 (99-05) > 323Ci
E46 (99-05) > 323i
E46 (99-05) > 325Ci
E46 (99-05) > 325i
E46 (99-05) > 325xi
E46 (99-05) > 328Ci
E46 (99-05) > 328i
E46 (99-05) > 330Ci
E46 (99-05) > 330i
E46 (99-05) > 330xi
3 Series
E90 / E91 / E92 / E93 (06-13) > 323i
E90 / E91 / E92 / E93 (06-13) > 325i
E90 / E91 / E92 / E93 (06-13) > 325xi
E90 / E91 / E92 / E93 (06-13) > 328i
E90 / E91 / E92 / E93 (06-13) > 328xi
E90 / E91 / E92 / E93 (06-13) > 330i
E90 / E91 / E92 / E93 (06-13) > 330xi
E90 / E91 / E92 / E93 (06-13) > 335d
E90 / E91 / E92 / E93 (06-13) > 335i N54 (07-10)
E90 / E91 / E92 / E93 (06-13) > 335i N55 (11-13)
E90 / E91 / E92 / E93 (06-13) > 335is N54
E90 / E91 / E92 / E93 (06-13) > 335xi N54 (07-10)
E90 / E91 / E92 / E93 (06-13) > 335xi N55 (11-13)
5 Series
E39 (97-03) > 540i
7 Series
E38 (95-01) > 740i
E38 (95-01) > 740iL
E38 (95-01) > 750iL
X1 Series
E84 X1 (2013-2015) > X1 28i
E84 X1 (2013-2015) > X1 28i xDrive
E84 X1 (2013-2015) > X1 35i xDrive
X3 Series
E83 X3 (04-10) > X3 2.5i M54 (2004-2005)
E83 X3 (04-10) > X3 3.0i M54 (2004-2006)
E83 X3 (04-10) > X3 3.0si N52 (2007-2010)
Z Series
E85 / E86 Z4 (03-08) > Z4 2.5i M54
E85 / E86 Z4 (03-08) > Z4 3.0i M54
E85 / E86 Z4 (03-08) > Z4 3.0i N52
E85 / E86 Z4 (03-08) > Z4 3.0si N52
E85 / E86 Z4 (03-08) > Z4 M