Nock & Insert Fitment Finder
Picking the right shaft is only half the job. Fitting a nock and an insert to it that actually seats right is the part most guides skip straight past. Pick your shaft — or its diameter class — and get the bore size, nock system and insert hardware that matches it.
ArcheryEra's calculators are built and maintained by a mechanical engineer with 8+ years of archery-domain experience. Models, assumptions and limitations are shown, not hidden.
Want to see exactly where the bore-size and nock-code figures came from? Read our Methodology & Assumptions →
Quick Tools
Same taxonomy as the Shaft Finder, one layer deeper
Every hunting shaft on the market fits one of three bore classes. Pick your shaft from the Arrow Shaft Finder’s own 18-model list, or enter the class or measured ID directly.
Pre-Sets
Four common situations, loaded at once. Everything stays editable once one is loaded.
Pick one to load a real shaft, then change anything from there.
Useful? This one is free, and staying free. If it saved you a returned-and-reordered insert pack, you can put a coffee towards the hosting.
Buy Me a Coffee🗣️ Shooting a shaft that isn’t in the 18-model list? Tell us its bore size and we’ll add it.
Join r/ArcheryEra →Pick your shaft
Same 18 real, currently-sold hunting shaft lines as the Arrow Shaft Finder. Picking one here sets the diameter class below automatically.
Or set the diameter class directly
Don’t see your shaft? Enter its measured bore ID
Leave at “off” to use the class buttons above. Slide it to override with your own number — this snaps to the nearest class and flags it if the number sits ambiguously between two.
What you need
⚠ Hybrid (FMJ) construction detected
⚠ Off-catalog bore size
Your typed ID sits close to the boundary between two classes. Treat the match below as a starting point and confirm against your shaft’s own spec page before ordering hardware.
What actually fits
Insert / bushing
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Nock
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📊 1-Minute Decision Matrix — all three classes
| Class | Bore ID | Nock | Insert / bushing | Limitation |
|---|
Guide
Matching Nocks & Inserts to Your Shaft's Diameter Class
Picking the right spine gets most of the attention. The step right after it — making sure the nock and insert you order actually fit the shaft's bore — gets skipped until an order arrives that doesn't seat. Here's how the sizing actually works.
Why Diameter Class, Not Brand, Decides Fitment
A shaft's nock and insert compatibility is set by its internal bore diameter, not by which company made the arrow. Manufacturers standardize around a handful of bore sizes so that component makers — nock brands, insert brands, broadhead brands — only need to build a few product lines rather than one per arrow model. Easton's own bushings catalog is organized exactly this way: bushings sold by shaft diameter (4mm, 5mm, 6.5mm), not by shaft model name.
The Three Classes, and What Nock Code Goes With Each
Feradyne's published Nockturnal nock-to-ID chart maps a letter code to each bore size, and it's a useful cross-brand reference even if you're not buying a lighted nock: G nocks fit a .165in bore, X nocks fit .204in, and S or GT nocks fit the .244–.246in standard bore, depending on the exact shaft. Cross-referencing that chart against Easton's own component names confirms the same three-way split: 4mm shafts pair with 4mm Uni Bushings and G-size nocks, 5mm shafts with 5mm Uni Bushings and X-size nocks, and 6.5mm shafts with 6.5mm Super Uni Bushings and S or GT nocks.
How Do I Find My Nock's Throat Size If I Don't Know My Shaft's Bore?
Archers hit this exact wall often enough that it's a recurring topic on the forums — a long-running ArcheryTalk thread exists specifically to crowd-source nock throat sizes by shaft model, because manufacturer spec pages don't always spell out the bore ID in plain language next to the shaft's marketed diameter name. The shortcut: a shaft marketed as "5mm" or ".204" is naming its bore, not its outer wall thickness, so the marketed name is usually the fastest path to the right class without a measurement at all.
Common Pitfalls
- Assuming "4mm" and "5mm" describe outer diameter. They describe the insert bore. A 4mm-class shaft's actual outer diameter can measure anywhere from roughly .22in to .25in depending on wall thickness and material — it's the bore, not the outside, that decides fitment.
- Treating FMJ shafts like plain carbon of the same bore number. Easton's aluminum-carbon FMJ line bonds a metal jacket around the core and uses its own HIT insert system and a Broadhead Alignment Ring — a generic bushing sized only to the numeric bore class is not built for that interface.
- Buying a broadhead sized for a different class and expecting a clean thread. The broadhead threads into the insert or outsert, not the shaft — mismatch the insert class and no amount of force makes the head seat correctly against the shaft's end.
Frequently Asked Questions
What's the difference between an insert and an outsert?
An insert glues inside the shaft's bore; an outsert slides over the outside of the tip instead, which is more common on the thinnest micro-diameter shafts where the carbon wall is too thin for a reliable internal glue joint alone. Both end in the same standard point thread.
Do nocks and inserts from different brands interchange within the same class?
Generally yes — a .204in nock fits a .204in bore regardless of which shaft brand made the arrow, since the class is a physical bore measurement, not a brand-specific standard. Hybrid-construction shafts (see FMJ above) are the exception.
My shaft isn't in the 18-model reference list — what do I do?
Enter its bore ID from the manufacturer's own spec page into the measured-ID slider above. Most current hunting shafts, including ones outside this tool's own reference list, are built to one of the same three standardized bore classes.
Under the hood
How far can you trust this match?
This is a lookup tool, not a physics model — every figure is either the exact same diameter-class bucket already published on the Arrow Shaft Finder, or cross-checked directly against Easton's own bushings catalog and Feradyne's published Nockturnal size chart (both linked in the guide above). What it can't do is confirm a specific SKU's exact bore to the thousandth of an inch — always cross-check against your shaft's own spec page before ordering hardware, especially on a hybrid-construction (FMJ) shaft.
Where each number came from Four entries — tap any one for the exact source
The three bore classes and their ID figures Not invented for this tool — the same buckets the Arrow Shaft Finder already publishes
Micro/4mm (.165–.166in), Small/5mm (.204in) and Standard/6.5mm (.244–.246in) are the exact same three diameter-class buckets already used on the Arrow Shaft Finder, built from the 18 real hunting shaft lines' own manufacturer spec pages. This tool adds the nock and insert layer on top of that existing classification rather than inventing a fourth bucket that would contradict it.
The nock letter codes and their ID figures Cross-checked against Feradyne's own published chart
G = .165in, X = .204in, S = .244in and GT = .246in come directly from Feradyne's published Nockturnal nock-to-ID compatibility chart, which lists these letter codes against hundreds of specific arrow models by name. It's a lighted-nock manufacturer's chart, but the letter-code-to-ID mapping is a physical fitment fact independent of whether the nock happens to light up.
The insert/bushing product names Read directly off Easton's own components catalog
"4mm Uni Bushing," "5mm Uni Bushing" and "6.5mm Super Uni Bushing" are Easton's own current product names, confirmed on Easton's bushings product category page, which also confirms the G/X/S nock pairing for each (listed directly in each bushing's own product description). The HIT (Hidden Insert Technology) and Broadhead Alignment Ring references for FMJ hybrid-construction shafts come from the same source.
How the “ambiguous” flag on a measured ID is decided Nearest-class snap, with a tie-break threshold instead of a false-confident guess
Typing a measured bore ID snaps to whichever class center (.1655in Micro, .204in Small, .245in Standard) it's closest to. If the two closest classes sit within .012in of each other — a gap smaller than a typical pin-gauge step — the match is flagged ambiguous instead of silently picking the nearer one, since a measurement error that small is well within normal caliper or pin-gauge tolerance. A .185in reading, for example, sits almost exactly between Micro and Small (a .0005in difference between the two candidate distances) and gets flagged rather than guessed.
Bore classes and nock/insert names are current as of this page's last update. Component lines change — always confirm against your shaft and hardware manufacturers' own current spec pages before ordering.
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Every free calculator on ArcheryEra in one table — answer a single question with a Quick Tool, or chain a full build through the Simulation Lab.
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| Nock & Insert Fitment FinderYou are here |
Your turn
Join the Conversation
Shooting a shaft that isn't in the 18-model list, or found a nock/insert combo that didn't match what's shown here? Tell us the shaft and the real bore size — that's exactly what keeps this table accurate.