Lemoyne: My understanding is the half moon nocks are needed on xbows that have claws that pivot below the rail/arrow. The ones that pivot above the rail/arrow like Excal and 10 pt use the flat nocks. My understanding is you can use the moon nocks on any bow, but your accuracy will be better if the mfgr calls for flat nocks and ya go w/ that. I believe both Barnett and Horton call for the moon nocks, not sure about others like Parker or Great Lakes. The reasons for all of this are that the above the rail pivot pushes the string down onto the rail, and the below pivots tend to want to raise the string above the rail briefly. Hope this helps.