I use B-50 on all the bows I make. I have used B-55 also. They are similar with one being slightly thinner than the other but not by much. I build 14 strands, Flemish twist with a bowyers knot on the bottom for bows of 45# and over(12 for under). It is a bit overkill but I've never had a string break and my bows shoot fast enough and smooth enough for me.