You want to put a round polyester in the cross. Shaped polyesters will chew up the NG in very little time. Good round pre-stretched polyesters are Kirschbaum Pro Line II series. Head Rip Control while not a polyester is also good. You do want the crosses to last as long as the NG. If they lose tension too fast, your NG is toast since you cannot re-tension the NG again, too short.