What tool do I need to remove knock sensor?

[Gelbster]

The fastener head in the photo is an " E " & you need an E socket for it.
My 2001 M96 did not have the E-head fastener.
The instructions for my new knock sensors assumed(?) it was being bolted onto an iron block and the torque spec would have stripped the threads on the M96. Be careful and consider substituting a s/s stud+nut if you want over 10Nm torque.Bee very careful where you apply silicone!