Nissan RB Twin-Cam 24V head drain AN-10 fitting that presses directly into the core plug at the back of the cylinder head and would be used with an AN-10, 90 degree return to the sump.
The RB head drain is an important part of the high performance application of these engines, as it serves two purposes; both to drain oil back to the sump, but also to relieve crankcase pressure to help oil returning to the sump through the other galleries.
