Mystery grease fitting problem

[TomC750]

My '41 Mercury was missing the grease fittings on both the front and rear springs. They are of an odd thread size. I bought new ones from Third Gen Auto. They included new extender nuts which I did not need as the old ones were present. Now comes the problem - Because the extender nuts (both old and new) have slots on the threaded id, the grease extrudes through this path as I would expect it to do being that there is no way the grease fitting will seal against the extender nut. What am I missing here?