My old blacktail strings are D 97 the new offered are D75 what's the :dunno: difference if any?
D75 is Brownell's copy of BCY's Dynaflight '97. BCY only uses DSM's "Dyneema" brand of HMPE, one of the most respected brands in the fiber industry.
Practical differences...couldn't say. A lot depends on where the fibers came from. DSM requires the label to recognize them if the material is made with their fibers.
My guess is that you will not notice the difference in the material, although you could end up getting totally different strand cound and serving. Those will make more difference than D75 vs DF97.
Could be they changed string makers. The best 100% HMPE string material on the market today is 8190F, made with SK90 Dyneema.