The Arizona Z Nock uses a snap-on design for a positive string fit, resulting in a smooth release from the bowstring. The main difference between the Z Nock and the Plastinock is the Z Nock's larger finger pinch area, allowing you to nock your arrows quickly and easily. The angled throat design keeps the nock on the bow string at any string angle, and the thin base blends perfectly to the arrow shaft. Fits all 9/32" diameter shafting. Also a great fit for 1916 aluminum shafts. Weigh 10 grains each.