You want a little wiggle room between the nock sets so at full draw they are not pinching the nock. I was also thinking that the guys who don't advovate the dual nock set have a friction fit to there nocks because they are scared of the nock falling off the string, but that is only necassary for self nocks. On a snap on nock the snap should occur right when the arrow is put on the string and then there should be zero bite on the serving in the throat. That is it should slide freely up and down the string without the nock points to stop it. This allows the string to rotate and forgives some torque. I am a firm believer that the difference in marginal archers and good ones is not all skill, the good ones have just figured out tricks to mitigate their errors.