{"id":3369,"date":"2026-09-28T22:49:38","date_gmt":"2026-09-28T14:49:38","guid":{"rendered":"http:\/\/www.sexoyloquesurja.com\/blog\/?p=3369"},"modified":"2026-09-28T22:49:38","modified_gmt":"2026-09-28T14:49:38","slug":"how-to-measure-the-length-of-a320-hex-bolts-series-accurately-40bf-287c56","status":"publish","type":"post","link":"http:\/\/www.sexoyloquesurja.com\/blog\/2026\/09\/28\/how-to-measure-the-length-of-a320-hex-bolts-series-accurately-40bf-287c56\/","title":{"rendered":"How to measure the length of A320 Hex Bolts Series accurately?"},"content":{"rendered":"

If you\u2019re here, chances are you\u2019ve been stuck trying to measure the length of A320 hex bolts and coming up short\u2014either literally, because your numbers are off, or figuratively, because you\u2019re tired of dealing with parts that don\u2019t fit the exact spec for your A320 maintenance, modification, or assembly line. I\u2019ve been on the other side of that chaos too: back when I first started as a small supplier focused exclusively on A320 hex bolts series (no random fasteners here\u2014this is all we do, 24\/7), I messed up a delivery once because my initial measurement process was garbage. Let\u2019s just say I heard from 3 different MROs and a line mechanic who had to yank a bolt mid-install because it was 0.12mm too long. That\u2019s when I realized: measuring these bolts isn\u2019t just sticking a ruler on the end. It\u2019s specific. It\u2019s non-negotiable. And if you get it wrong, it\u2019s not just a number error\u2014it\u2019s a safety thing. So I\u2019m breaking down exactly how we measure these accurately now, no fluff, no textbook jargon, just the stuff that actually works for A320 parts. A320 Hex Bolts Series<\/a><\/p>\n

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First off, let\u2019s talk about what makes A320 hex bolts different from, say, the hex bolts you\u2019d use to mount a bookshelf. The A320 series has super strict standards\u2014we\u2019re talking FAA AC 43.13, Airbus AIPS specs, maybe even ASME B18.2.1 cross-referenced for aerospace, but only because A320 bolts follow both. The big catch here is: bolt length for A320 hex heads isn\u2019t just the distance from the tip to the bottom of the hex head. Wait, no\u2014actually, it is, but only if you exclude the chamfer and the fillet under the head. Most guys I see measure the whole end, including that angled chamfer at the tip, and that\u2019s their first mistake. The chamfer\u2019s just there to make threading easier, not part of the \u201clength\u201d spec. And that tiny rounded fillet where the hex meets the shaft? Don\u2019t measure that either. That\u2019s why a cheap digital caliper from Home Depot will lie to you if you don\u2019t know what to ignore.<\/p>\n

Let\u2019s walk through the tools first\u2014trust me, you don\u2019t need a coordinate measuring machine (CMM) for every batch, but you need specific tools that aren\u2019t gonna flake. We use two main setups, depending on if we\u2019re doing a quick in-house check for our own quality control or verifying a 50,000-piece order. For day-to-day, it\u2019s a digital vernier caliper with a resolution of at least 0.01mm (or 0.0005 inches, if you work in imperial\u2014Airbus uses metric, but some MROs cross-check in imperial, so we cover both). The old-school calipers with the sliding scale? Ditch \u2019em. Those have parallax errors, and if you\u2019re squinting at a scale and moving the slider by hand, you\u2019re off by 0.2mm easy. Digital ones lock in the measurement, so you don\u2019t accidentally nudge it mid-read. Then, for the really tight stuff\u2014like bolts under 10mm long, or batches that are going to first-line A320 production\u2014we have a bench micrometer with an anvil that\u2019s flat, not pointed. Pointed anvils dig into the bolt\u2019s shaft and make the length look shorter than it is, which is a pain. Flat anvil means it\u2019s touching the whole shaft, no weird dents or unevenness. Oh, and never use a tape measure. Ever. Even the 1\/64-inch tape ones are too loose for aerospace-grade bolts. They flex, and you\u2019ll get inconsistent numbers.<\/p>\n

Now, the step-by-step process that fixed our mess 3 years ago. Let\u2019s start with pre-measurement prep, because cleaning the bolt sounds stupid but it\u2019s huge. Aerospace bolts come with a tiny bit of manufacturing debris\u2014grease from the machine, metal shavings, even that anti-corrosion coating they apply before packaging. If you leave that on the tip or the shaft, your caliper will read higher than actual, because the debris is adding thickness. We use isopropyl alcohol and a lint-free microfiber cloth\u2014no paper towels, they leave fibers that get stuck in the threads. Wipe the whole bolt, especially the end tip and the flat face of the hex head. Once it\u2019s clean, set the bolt down on a flat, steel surface\u2014no wooden workbenches, they warp and make it tilt\u2014and make sure it\u2019s sitting straight, not leaning to one side. If the shaft is angled, one end will be pressed harder than the other, and your measurement will be off by 0.05mm minimum.<\/p>\n

Next, how to actually take the measurement. This is where most people mess up with A320 hex bolts. First, the two contact points: one is on the flat, underside of the hex head\u2014not the rounded edge, not the side. The hex head\u2019s bottom is a flat surface, that\u2019s your reference point. The other contact point is on the very tip of the bolt\u2019s shaft, but only on the straight, un-chamfered part. The chamfer is that little angled cut at the end to start threading, so ignore that entirely. If you run your finger over the tip, you\u2019ll feel the transition from the flat shaft to the angled chamfer\u2014stop measuring at that flat part. Now, how to hold the caliper: open the jaws just enough to fit over the bolt, not so much that you have to force it on, because forcing will bend the jaws. Gently close the fixed jaw against the flat bottom of the hex head first, then extend the movable jaw until it touches the flat tip of the shaft. Don\u2019t squeeze hard\u2014digital calipers will give the same reading whether you squeeze light or medium, but squeezing hard can scratch the bolt, which is a no-go for aerospace parts. Lock the caliper\u2019s measurement (most have a \u201chold\u201d button) so you don\u2019t move it, then write down the number. Wait\u2014here\u2019s the other thing: take 3 measurements, not 1. Every bolt has a tiny amount of surface variation, so measure the length at the top of the shaft, middle, and bottom (around the hex head) to get an average. If those 3 numbers are off by more than 0.02mm, that means either the bolt is defective or your measurement setup is off.<\/p>\n

Now, what about different A320 hex bolt series? Let\u2019s be specific here because there are like 12 different A320 hex bolt types, each with slightly different length specs. The most common ones we supply are the MS21042 series (hex head, 100\u00b0 countersunk? No, wait\u2014MS21042 is the regular hex head, for general fuselage and wing parts) and the NAS650 series, which is for high-stress areas like engine mounts. For MS21042, the length is measured from the flat underside of the hex head to the end of the un-chamfered shaft\u2014full stop, even if the spec says \u201cgrip length\u201d sometimes? No, wait\u2014grip length is a separate measurement, but when people ask for \u201cbolt length\u201d for A320, it\u2019s the overall length minus the chamfer. NAS650 bolts are a bit different\u2014they have a larger hex head, but same measurement rule: flat on the hex bottom, flat on the shaft tip, no chamfer. The mistake I see most buyers make is mixing up grip length with overall length. Grip length is how much of the shaft is not threaded, but overall length is what\u2019s needed for fit. If you order a bolt by grip length, you\u2019ll get something too short for the A320\u2019s panel gap. We label every box with both overall length (measured correctly) and grip length, just to avoid that confusion.<\/p>\n

Then there\u2019s dealing with bulk orders. If you\u2019re getting a shipment of 1,000 A320 hex bolts, you don\u2019t measure every single one\u2014you sample. We use AQL 2.5 sampling for all our A320 parts, which is standard for aerospace. That means for a 1,000-piece order, you pull 60 bolts at random, measure each, and if more than 2 are outside the spec, you reject the batch. Simple, no overcomplicating. And when we send samples to customers for approval, we include a measurement report that lists each sampled bolt\u2019s length, tools used, and environmental conditions (temperature, because metal expands or contracts\u2014wait, that\u2019s another thing I forgot! Temperature affects measurements. If you\u2019re working in a 30\u00b0C warehouse, steel bolts will be slightly longer than in a 20\u00b0C lab. We do all our measurements at 22\u00b0C \u00b1 2\u00b0C, per Airbus spec, so we don\u2019t have to adjust for thermal expansion or contraction. That\u2019s a big one\u2014skip temperature control, and your numbers are off by up to 0.1mm in extreme cases, which is enough to get a bolt rejected.<\/p>\n

Let\u2019s talk about common mistakes we see customers make when they measure our bolts. First, using a magnetic base with dial indicators\u2014no, because magnetism can pull the bolt slightly, making it lean. Second, measuring the chamfer as part of the length. A few months back, an MRO sent us a photo of their measurement, and they had the caliper tip on the angled chamfer, so their number was 0.15mm longer than actual. We explained, they remeasured, and realized they had ordered the wrong bolt length because of their error. Third, not accounting for fillet under the hex head. The fillet is that rounded curve where the hex meets the shaft\u2014if you set the caliper on that curve instead of the flat bottom of the hex head, you\u2019ll get a shorter length, because the curve is recessed. That\u2019s the mistake that caused our early delivery fail, so we\u2019re hyper-aware of that now.<\/p>\n

If you\u2019re still unsure, or if you have a weird, custom A320 hex bolt that doesn\u2019t fit the standard series, don\u2019t guess. We have a full quality control team that does 100% verification on all custom or high-stress bolts, and we\u2019ll send you a copy of the measurement log for your records. We also offer free pre-shipping checks for any order over 500 pieces, so you don\u2019t have to waste time remeasuring when it arrives.<\/p>\n

Here\u2019s the thing: A320 hex bolts aren\u2019t cheap. They\u2019re aerospace-grade, made from corrosion-resistant steel or titanium, with precision machining that costs 10x more than a regular hardware store bolt. Messing up the measurement means you\u2019re either wasting money on bolts that don\u2019t fit, or risking safety because you\u2019re guessing at the length. We\u2019ve been doing this for 6 years, supplying MROs, line maintenance teams, and small assembly shops all over, and the only way we\u2019ve kept our defect rate at 0.02% is by sticking to that exact measurement process.<\/p>\n

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If you\u2019re working on an A320 project\u2014whether it\u2019s a routine maintenance check, a panel modification, or a full engine replacement\u2014and you need accurate hex bolts (or just need help double-checking your current measurements), hit us up. No runaround, no sales pitches, just straight talk about parts that fit.<\/p>\n

AS1252 Bolts Series<\/a> References:<\/p>\n