dsc98404.jpg

Detail of the third injector.

Picture 2 of 2.

Note the three closely-spaced holes; the middle hole in this set is an index hole. The F-1 injector is indexed via two pins, one round and one diamond shaped, which fit into two index holes located 180° apart to ensure that the injector is installed in the proper orientation.

Both index holes are round, although they are different sizes; I believe that the diamond-shaped pin has a larger diameter.

This index hole has a larger diameter than the other holes, and so I believe it is for the diamond-shaped index pin.