I have milspec 6C4's brand new sealed in their as issued box's these are the
one's called for in the original parts list for the R390A. Interestingly the
boxes on mine are miss-printed 64C instead of 6C4. The Tube it's self is
marked 6C4, no W, or WA, just JAN (Joint Army Navy) 6C4.
Ken de W7ITC