When Dacron was the only bowstring material used, almost every nock commercially available would fit snugly on a bowstring. Today many bowyers are building bows that can shoot Fast Flight or other non-stretch string material. These new materials are much stronger and much thinner than Dacron, so a smaller number of strands are necessary to build a bowstring of similar strength to Dacron.
To test your nock’s fit to the bowstring, nock an arrow on the serving pointing down. Give the bowstring a sharp, but light, tap and the arrow should just release from the string. If it stays attached you will have to open the nock slightly. If the arrow falls off on its own or if the nock slides up and down on the serving, your nock is too loose and will need to be adjusted tighter.
To adjust the throat of a plastic nock simply place it in a cup of very hot water. Let it set for about ten to twenty seconds, and then place it on your bowstring and pinch to fit, holding it there until it cools. By all means DO NOT bite a nock to tighten it’s grip. Doing so may weaken the tangs of the nock, possibly creating a fracture that will give way when the arrow is shot and cause you to dry fire your bow. If hot water is not available, use a butane lighter, with the flame well away from the nock, and warm it up enough to adjust the fit.