On this bows it is B50, But nowadays usually BCY 425 X
Here is my answer in your thread about FF:
I also switched from B50 to FF. In some cases, especially with lower dense wood, no good results (damaged bows). So one day I found BCY425X, and IMO this is a very good material with no creep and a bit of stretch witch is essential for primitve bows. Now I make all my strings with this material, strengthen it up at the ears with some short additional B50 leftovers. My strings are very thin, for example only 1,3 mm for a 70# bow, using2 x 6 strands.
There are allot of different FF out on the market, I'm interested what you guys are using ...
skins are diamond back
simson