*Why "D4"?  I normally get asked,  and gets jumbled with A5 (that's a climbing grade), and D5 (which stood for "Deuce5"), two models I are actually involved with in the past.  My nickname in Yosemite was "Deucey", https://jadavqxl886998.mpeblog.com/52164809/d4-can-be-fun-for-anyone