Arrow Nock Size Chart: Groove & Throat Specs for 44 Nocks by Shaft ID

A nock has to fit twice: its shank has to match your shaft's inside diameter (.166″, .204″, .233″ or the .244–.246″ family), and its groove has to match your bowstring's center serving. For the string side, the serving should measure larger than the nock's groove (so it snaps on) but no larger than its throat (so the string can slide out clean). Across the 44 nocks below, published grooves run from 0.074″ to 0.105″ and throats from 0.098″ to 0.120″. That spread is why a nock that clicks perfectly on one string falls off another.

Does Your Nock Fit Your String? Check It in 30 Seconds

Pick your nock (or type in its groove and throat), enter your center-serving diameter from a caliper, and the check tells you where the serving sits between the nock's groove, where it snaps on, and its throat, where it rests. Not sure how to measure? The four-step method is right below the tool.

How Do You Measure Your Center Serving?

1. Measure where the nock actually sits. On a release bow that's the short stretch of serving between your D-loop knots, not the serving above or below them.
2. Close the caliper jaws gently. Serving is soft and flattens under pressure, and a hard squeeze can read a couple of thousandths small, which is the whole width of some snap windows.
3. Take two readings 90° apart and average them. A served string is rarely perfectly round.
4. Measure after break-in. OCD Strings tests fit only after the center serving has settled, and so should you.

No caliper? Skip the numbers and use the hang-and-tap test plus the troubleshooting table further down. It tells you which direction to move (smaller or larger groove), just not by how much.

Where Do These Numbers Come From?

I wrote this after the same question kept showing up in threads like a recurve shooter whose .246 Gold Tip nocks were loose on a new 16-strand string, an ArcheryTalk request for a nock fitment chart that lists throat sizes, and another asking which center serving size goes with which nock. Nobody in those threads had a single table that put the string side and the shaft side in one place, so I built one from Lancaster Archery's published groove and throat measurements, cross-checked the lighted-nock weights against each maker's own product pages, and put a calculator on top.

What Do "Groove" and "Throat" Actually Mean on a Nock?

Look into the slot of any modern nock and it narrows before it widens. That narrow point is the groove: the lips the serving has to squeeze past, and the reason you hear a click. Behind it sits the throat, the rounded seat the string rests against while you draw and the surface it slides off at release.

So the fit window is simple geometry. Serving smaller than the groove? No click, no retention. Serving bigger than the throat? The ears stay spread around the string the whole time, and the string has to drag its way out.

Arrow Nock Size Chart: Which Nock Fits Which Shaft ID?

Sorted by the bore each nock is made for, then by maker. Groove and throat are Lancaster Archery's published measurements. The last column is mine: throat minus groove, in thousandths of an inch. I call it the snap window, and it tells you how forgiving a nock is of serving variation. A wide window tolerates a range of servings; a narrow one wants a serving sized for it.

Groove and throat values from Lancaster Archery's nock measurement table; snap window is my own subtraction. Beiter insert nocks (#1, #1H, #2, H) share the groove and throat of the matching pin nock. Lancaster lists every standard-diameter nock as ".245" fit; the makers split that family into .244″ and .246″ parts (see the next table), so check your shaft's own published ID before you order.

Can You Mix Nock Brands on the Same Shaft ID?

Usually, yes, as long as the nock is made for your shaft's exact published bore. Lancaster's guide says outright that many nocks cross over between arrow brands, and the table above bears it out: every .204″ nock listed shares one shank size. Where people get caught is the standard-diameter family, because .244″ and .246″ get lumped together as "6.5mm" when they're not the same hole.

Not sure which bore class your shaft is in? The Nock & Insert Fitment Finder maps 18 current hunting shafts to their nock and bushing sizes. This page handles the other half of the fit: nock to string.

How Different Are the .204 Nocks, Really?

The .204″ class is where most modern hunting arrows live, so I plotted the snap window of all seven .204 nocks on one scale. Each bar runs from the nock's groove to its throat. A serving diameter drawn as a vertical line through the chart shows which nocks will click on it, which won't, and which will clamp it.

Two things jump out. The Bohning A has a 22-thousandth window, twice that of the Accu-Tough and the Black Eagle R, so it accepts the widest range of servings of anything in the class. And the Gold Tip and Black Eagle nocks sit high: their grooves (0.104″ and 0.103″) are bigger than the throat of some small-groove nocks elsewhere in the chart. Switch from Easton X to Accu-Tough on the same string and a crisp click can turn into no click at all.

Beiter #1 vs #2: What's the Actual Difference?

Ten thousandths of an inch. The #1 groove measures 0.088″ with a 0.106″ throat; the #2 measures 0.098″ with a 0.118″ throat. Lancaster's guidance is that the #1 suits thinner serving, roughly 12 to 16 strands of string depending on material, and the #2 suits thicker serving, roughly 14 to 18 strands. Those ranges overlap on purpose, because strand count alone doesn't set the serving diameter. Serving material and winding tension do too.

The other difference matters just as much on a recurve. The standard #1 and #2 are asymmetric: built for a finger release and meant to be installed facing a set direction. The H and #1H versions are symmetric, for release-aid shooters. Beiter's nock datasheet notes that each size comes from a single mold, which is why a Beiter nock tends to match its neighbor in the bag so closely.

Which Nock-Fit Test Should You Trust?

Three reputable sources describe three slightly different tests, and they don't contradict each other so much as target different shooters.

Notice the rotation disagreement: Bow International wants a nock that turns, OCD Strings wants one that doesn't. That isn't sloppiness. Finger shooters roll the string at release, and a nock that grips can get twisted with it; a D-loop shooter wants the arrow locked in orientation. Pick the test that matches how you shoot.

Does Cold Weather Tighten or Loosen Nock Fit?

Cold weather gets blamed for a lot of fit problems, and the usual explanation is that plastic nocks shrink. I ran the math on that. Polycarbonate's linear thermal expansion coefficient is 65 to 70 millionths per degree Celsius. Take a 0.100″ groove from a 70°F shop to a 0°F stand: that's 38.9°C of cooling, and 0.100 × 0.0000675 × 38.9 ≈ 0.0003″ of shrinkage.

Put that next to the other numbers on this page. It is one-seventh of the ±0.002″ disagreement between published specs for the same nock, and one-thirtieth of the difference between a Beiter #1 and #2. The serving shrinks in the cold as well, which cancels some of it. And the same polycarbonate data lists a lower working temperature of −40°F.

What Makes a Nock Pinch the String at Release?

A pinch means the string can't leave the nock freely. From the sources above there are three mechanical causes, in order of how often they're the answer:

1. Serving at or above the throat. The ears never close back around a free-sliding string; they clamp it. Run your caliper number through the Nock Fit Check.
2. Nocking points too close. Easton recommends 1–2 mm of clearance between the bottom of the nock and the top of the bottom nocking point. Clamped between two brass or tied points, even a correctly sized nock can't release clean.
3. An asymmetric nock turned the wrong way. On a finger bow, a standard Beiter #1 or #2 is built to face a set direction. The symmetric H versions don't have this problem.

A pinched release also shows up in tuning. OCD Strings points out that a nock that holds on too long can make the arrow behave as if it were stiffer than it is, so fix fit before you chase a paper tear with the Paper Tune Root-Cause Diagnostic.

What Cracks a Nock, and When Should You Replace One?

No nock maker I found publishes a shot-count life. So I won't give you one. What the manufacturers do document is what cracks nocks, and every item on that list is an event you can spot:

• A damaged pin. Easton: a scored or dented nock pin can cause stress cracking of the nock, and should be discarded and replaced.
• A fit that's too tight. Bow International warns a tight nock can crack over time and fail during a shot. That's the serving-above-throat case again.
• Chemicals. Easton lists cleaning solvents, gasoline and DEET-type insect repellents as things to keep off polycarbonate nocks. Worth knowing in bug season.
• Bent ears. Easton and Bow International agree: never bend nock ears to change the fit.
• Impacts. A hit from another arrow is the obvious one, and the reason to check nocks after a tight group.
• Tools. Easton: no pliers (and no teeth) for installing or turning nocks. Use a nock tool.

⚠️ Why a Cracked Nock Is a Dry-Fire Risk

Easton warns that a poor fit can let the nock "squirt" off the string and cause a dry fire. A cracked nock is worse, since it can split at full draw. Inspect nocks after every shooting session and after any impact, which is Easton's own interval, and flex each one gently while you look for cracks, spread ears or a nock that turns loose in the shaft. Replace anything doubtful. A dozen nocks is a small thing to throw away next to a bow's limbs.

How Much FOC Does a Lighted Nock Cost You?

A lighted nock puts its extra weight at the worst possible spot for FOC: the very back of the arrow. I ran a common hunting build through the site's FOC engine: 28″ shaft at 8.5 grains per inch, 12-grain insert, 100-grain point, three 8-grain vanes. Weights are from each maker's product page.

Two points of FOC off a 16-grain change, while the arrow gets heavier. On a heavier build (29″, 9.5 gpi, 25-grain insert, 125-grain head) the same swap moves FOC from 13.5% to 11.4%. At the 1-fps-per-5-grains shop rule, 16 extra grains also costs about 3 fps. I'd call neither number a deal-breaker for a hunter who wants to see the hit, but both are worth knowing before you tune broadheads, not after. I couldn't find a manufacturer-published weight for Firenock lighted nocks, so they're not in the table.

Does a Lighted Nock Fit Your String the Same Way?

Not necessarily. A lighted nock has its own molded groove and throat, and I couldn't find published groove or throat sizes for Nockturnal, Lumenok or Firenock nocks, so none of them are in the size chart above. Treat the switch like a new nock: hang-and-tap test every lighted nock on your actual string before it goes in the quiver.

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