I feel 1/2" is the safest for yew. Its not so much the width, as the softness of the wood at the nocks. They need to be deep enough so they really hold the string on. I also don't like a sharp edge near the back for the nocks. I have had a couple of yew bows split off one side of the nocks when getting a normal brace height bow string on.
Pin nocks are probably the strongest of self nocks.
A decent set of hardwood, or horn overlays, or full horn nocks are my preference with yew.
