don't know but they have wrapped loops and I opt for the installed silencers and they are quiet, to me they sound like a low braced B50 recurve. I also went max on the brace for stability and I still gained more speed.
I'm ordering one for my 52# alleghany MTN bow because even though it bare shafts the same arrow as my 50# palmer recurve it hits about 5" lower in the target at 27yds (bare shaft tuned) where speed is a factor and the 570gr arrow with big shields runs out of gas after 20yds,,,, I really try to keep the bows here shooting the same arrows and keep bows based alot on that so I'm betting the SBD string will even things out between the two bows,,,,,, I wont get one for my Palmer Classic because I have about 80 Heritage arrows here all made up and I don't want to be messing with that many arrows,, the preditor only had 10 arrows before the string so it was my demo bow.
the strings really are Awesome! if you do not bare shaft your shafts then you might not even notice any flight difference but not sure about broadhead flight but if you do bare shaft your shafts you will notice a weaker spine after the new string, SO just max out the brace/fistmele and/or drop point weight then order a few more stirngs because you will not go back.