This is the large copper nut used to fasten the exhaust manifold/turbo to the cylinder head on N55 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 15 nuts per set.
Suit for
1-Series E82 / E88 (11-13) > 135i 135is N55

3-Series E90 / E92 / E93 (11-13) > 335i 335xi N55

2 Series
F22 / F23 (14-17) > M235i M235i xDrive N55
F22 (2019+) > M240i Racing N55
2 Series F87 (16-18) > M2 N55
3 Series F30 / F34 (14-15) > 335i 335i xDrive N55
4 Series F32 / F33 / F36 (14-15) > 435i 435i xDrive N55
5 Series F10 / F11 (11-16) > 535i 535i xDrive
6 Series F12 / F13 (12-18) > 640i
7 Series F01 / F02 (2009-2015) > 740Li 740i

X3 Series F25 X3 (2011-2017) > X3 xDrive35i N55
X4 Series F26 X4 (2015-2018) > X4 35i xDrive M40i xDrive
X5 Series E70 X5 (07-13) > X5 xDrive35i N55
X6 Series E71 X6 (2008-2014) > X6 xDrive35i N55 (10-13)