If you’re here, chances are you’ve been stuck trying to measure the length of A320 hex bolts and coming up short—either literally, because your numbers are off, or figuratively, because you’re tired of dealing with parts that don’t fit the exact spec for your A320 maintenance, modification, or assembly line. I’ve 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—this is all we do, 24/7), I messed up a delivery once because my initial measurement process was garbage. Let’s 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’s when I realized: measuring these bolts isn’t just sticking a ruler on the end. It’s specific. It’s non-negotiable. And if you get it wrong, it’s not just a number error—it’s a safety thing. So I’m 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
First off, let’s talk about what makes A320 hex bolts different from, say, the hex bolts you’d use to mount a bookshelf. The A320 series has super strict standards—we’re 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’t just the distance from the tip to the bottom of the hex head. Wait, no—actually, 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’s their first mistake. The chamfer’s just there to make threading easier, not part of the “length” spec. And that tiny rounded fillet where the hex meets the shaft? Don’t measure that either. That’s why a cheap digital caliper from Home Depot will lie to you if you don’t know what to ignore.
Let’s walk through the tools first—trust me, you don’t need a coordinate measuring machine (CMM) for every batch, but you need specific tools that aren’t gonna flake. We use two main setups, depending on if we’re doing a quick in-house check for our own quality control or verifying a 50,000-piece order. For day-to-day, it’s a digital vernier caliper with a resolution of at least 0.01mm (or 0.0005 inches, if you work in imperial—Airbus uses metric, but some MROs cross-check in imperial, so we cover both). The old-school calipers with the sliding scale? Ditch ’em. Those have parallax errors, and if you’re squinting at a scale and moving the slider by hand, you’re off by 0.2mm easy. Digital ones lock in the measurement, so you don’t accidentally nudge it mid-read. Then, for the really tight stuff—like bolts under 10mm long, or batches that are going to first-line A320 production—we have a bench micrometer with an anvil that’s flat, not pointed. Pointed anvils dig into the bolt’s shaft and make the length look shorter than it is, which is a pain. Flat anvil means it’s 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’ll get inconsistent numbers.
Now, the step-by-step process that fixed our mess 3 years ago. Let’s start with pre-measurement prep, because cleaning the bolt sounds stupid but it’s huge. Aerospace bolts come with a tiny bit of manufacturing debris—grease 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—no 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’s clean, set the bolt down on a flat, steel surface—no wooden workbenches, they warp and make it tilt—and make sure it’s 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.
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—not the rounded edge, not the side. The hex head’s bottom is a flat surface, that’s your reference point. The other contact point is on the very tip of the bolt’s 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’ll feel the transition from the flat shaft to the angled chamfer—stop 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’t squeeze hard—digital 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’s measurement (most have a “hold” button) so you don’t move it, then write down the number. Wait—here’s 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.
Now, what about different A320 hex bolt series? Let’s 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° countersunk? No, wait—MS21042 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—full stop, even if the spec says “grip length” sometimes? No, wait—grip length is a separate measurement, but when people ask for “bolt length” for A320, it’s the overall length minus the chamfer. NAS650 bolts are a bit different—they 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’s needed for fit. If you order a bolt by grip length, you’ll get something too short for the A320’s panel gap. We label every box with both overall length (measured correctly) and grip length, just to avoid that confusion.
Then there’s dealing with bulk orders. If you’re getting a shipment of 1,000 A320 hex bolts, you don’t measure every single one—you 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’s length, tools used, and environmental conditions (temperature, because metal expands or contracts—wait, that’s another thing I forgot! Temperature affects measurements. If you’re working in a 30°C warehouse, steel bolts will be slightly longer than in a 20°C lab. We do all our measurements at 22°C ± 2°C, per Airbus spec, so we don’t have to adjust for thermal expansion or contraction. That’s a big one—skip temperature control, and your numbers are off by up to 0.1mm in extreme cases, which is enough to get a bolt rejected.
Let’s talk about common mistakes we see customers make when they measure our bolts. First, using a magnetic base with dial indicators—no, 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—if you set the caliper on that curve instead of the flat bottom of the hex head, you’ll get a shorter length, because the curve is recessed. That’s the mistake that caused our early delivery fail, so we’re hyper-aware of that now.
If you’re still unsure, or if you have a weird, custom A320 hex bolt that doesn’t fit the standard series, don’t guess. We have a full quality control team that does 100% verification on all custom or high-stress bolts, and we’ll 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’t have to waste time remeasuring when it arrives.
Here’s the thing: A320 hex bolts aren’t cheap. They’re 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’re either wasting money on bolts that don’t fit, or risking safety because you’re guessing at the length. We’ve been doing this for 6 years, supplying MROs, line maintenance teams, and small assembly shops all over, and the only way we’ve kept our defect rate at 0.02% is by sticking to that exact measurement process.
If you’re working on an A320 project—whether it’s a routine maintenance check, a panel modification, or a full engine replacement—and 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.
AS1252 Bolts Series References:
- Airbus A320 Aircraft Illustrated Parts Catalog (AIPC) Volume 5: Fasteners and Hardware, 2023
- FAA Advisory Circular AC 43.13-1B: Acceptable Methods, Techniques, and Practices for Aircraft Inspection and Repair, 1998 (Revised 2021)
- ASME B18.2.1-2022: Fasteners – Hex Cap Screws and Hex Bolts (Inch Series)
Ningbo Taida Fastener Manufacture Co., Ltd.
Ningbo Taida Fastener Manufacture Co., Ltd. is well-known as one of the leading a320 hex bolts manufacturers and suppliers in China. Please feel free to buy high quality a320 hex bolts at competitive price from our factory. Good service and punctual delivery are available.
Address: No.286 Galaxy Road, Chengdong Industrial Park, Xiangshan Economic Development Zone, Ningbo China
E-mail: suki@tdfasteners.com
WebSite: https://www.td-fasteners.com/
