On the 7001s that I bought, most of the turnbuckles seem to have the hex-shaped adjuster section in the center of the turnbuckles. The vast majority of the replacement turnbuckles have a square-shaped center section, most of those having a notch on one end to identify the direction of the threads.
Am I correct in assuming that the hex shaped style is the oldest, with the square shaped without the notch being the middle, and the square shaped with the notch being the newest? If so, does anybody know when the changes occurred?
I'm almost done collecting a set of the square without notches, and now realizing that they probably aren't correct for the 7001 that I'm building.
