I have the same issue on one bow. I just got a new string for it so problem solved, but what I did before that and in the past on other bows, was to use Beman ICS solid color nocks. They have worked well for me on most medium and larger strings. They have good size base of nock area, but the ends of the nock can be a little tight. I put a screw driver in them as a wedge to open them up. It is best to heat them a little in boiling water first to soften them a little. Then wedge them open and cool them They are tough nocks. I have never broken one unless it has been split from an arrow. Even then they don’t break. Other translucent nocks and even some opaque nocks I have tried shatter when hit. I worry about spreading them, but not the opaque Bemans.