This is the large copper nut used to fasten the exhaust manifold/turbo to the cylinder head on N20 engines.
Copper deforms when tightened and subjected to heating and cooling so it should not be re-used.
This is replaced for BMW part number 18407502196 (18 40 7 502 196).

Sold 10 nuts per set.
suit for
2 Series
F22 / F23 (2014+) > 228i
F22 / F23 (2014+) > 228i xDrive
3 Series
F30 / F31 / F34 (2012+) > 328i
F30 / F31 / F34 (2012+) > 328i xDrive
4 Series
F32 / F33 / F36 (2014+) > 428i
F32 / F33 / F36 (2014+) > 428i xDrive
5 Series
F10 / F11 (11-16) > 528i
F10 / F11 (11-16) > 528i xDrive
X Series
F25 X3 (2011+) > X3 sDrive28i
F25 X3 (2011+) > X3 xDrive28i
X Series
F26 X4 (2015+) > X4 28i xDrive
X Series
F48 X1 (2016+) > X1 28i
F48 X1 (2016+) > X1 28i xDrive