It was in 1991 that the “Iceman” was discovered by hikers high up in the Italian Alps near the border with Austria.Among the artifacts recovered alongside his mummified corpse were an unfinished longbow, a quiver and a handful of arrows, only two of which were ready to be shot. They had leaf-shaped flint heads held in place within a notch by wood pitch and sinew; three trimmed feathers for fletchings; and notches cut into the back end to receive the bowstring.So archers have been using nocks of some fashion for more than 5,000 years, because the Iceman is believed to have died 5,300 years ago. Today, arrow nocks are much more sophisticated, but they still serve the same purpose.PRESS-FIT NOCKSPress-fit nocks arguably are the most common nock today, as they are used with nearly all but the skinniest carbon shafts. They’re also used with many aluminum shafts, too. As the category name implies, to install a press-fit nock, you simply slide the nock post inside the arrow shaft, and press down until the shaft end contacts the actual nock. No glue is required with press-fit nocks. You just stick them in, and pull them out, as needed.They are completely indexable, which means you can turn them to any position to align properly with your fletchings and to achieve rest and/or cable clearance for your fletchings.With press-fit nocks, it’s critical to know what shaft you’re shooting, since not all shafts have the same inside diameter. Naturally, all arrow manufacturers make nocks to fit their arrows. Aftermarket press-fit nocks bear the common sizes G, F, X, A, H, S and GT.G and F nocks fit shafts with a .166-inch inside diameter.X and A nocks fit shafts with a .204-inch inside diameter.H and H.E. nocks fit shafts with a .234-inch inside diameter.S nocks ‑ also called Super Nocks ‑ fit shafts with a .244-inch inside diameter.GT nocks fit shafts with a .246-inch inside diameter.Some archers will put aluminum Uni-bushings into the nock ends of their arrows in order to help protect the shafts from being damaged by other arrows. They then must find press-fit nocks that fit those bushings.Also, bowhunters use certain press-fit nocks with battery-powered lights inside that light up when an arrow is released. The lighted nocks help bowhunters recover game and/or their arrows in poor light.PIN NOCKSPin nocks are tiny nocks that fit onto an aluminum pin that’s installed into the nock end of the shaft. The pin bushings are meant to protect shafts from being damaged by other arrows. Any nock labeled as a “pin” nock will fit any pin insert, since all pins are a standard size.Pin nocks are popular among competition archers, who shoot expensive shafts they don’t want to get damaged. Also, target archers believe the smaller, more fragile pin nocks tend to be more accurate and they minimize deflections of their own arrows, which could result in an arrow getting pushed into a lesser scoring ring.OVERNOCKSThe overnocks are those attached to an arrow by sliding the arrow inside the nock. The nock fits over top of the shaft.Overnocks are most commonly used with carbon arrows and they come in nearly two dozen sizes to fit a host of shafts. They’re also used with shafts made of other materials. Easton’s X10 Overnock, for example, can be used with the company’s X10 aluminum/carbon shafts.CONVENTIONAL NOCKSThese nocks are used on aluminum arrows with the cone-shaped back ends, called the swage. They come in several sizes which correlate to shaft diameters. You can simply press these nocks into place and tighten by hand, or you can lock them in place with a non-cyanoacrylate glue.GROOVE SIZINGSome other nock references you need to be aware of are “small groove” and “large groove” sizings. The groove is the opening between the nock posts or ears. The small-groove nocks are meant for the skinnier bowstrings, like you’d find on low-poundage recurve bows. The large-groove nocks are meant for compound bows and for recurves with thicker strings.You want your nock to make an audible click when you seat the nock on the bowstring. Usually, you’ll only hear that click when the nock fits perfectly. You don’t want your nock to be too tight or too loose on the string.CROSSBOW NOCKSCrossbow nocks, obviously, are the nocks used with crossbow bolts. There’s the flat nock, the half-moon, the Omni-Nock – which features six micro-grooves that form three bowstring channels - and the Capture nock – which closely resembles a traditional arrow nock.Different crossbow manufacturers recommend different nocks for their bows. Check to see which one is recommended for the bow you’re shooting.The nock is the critical connection between your arrow and the bowstring. Know which one you need to get the job done right.