Hey there, fellow builders, fabricators, and random folks who’ve spent way too long staring at fastener specs (I see you). If you’ve ever picked up a 0 carriage bolt—you know, the kind with that classic round, smooth head and square shank under it that locks into wood or metal to keep it from spinning—you’ve probably had one question bug you at some point. I get it, because I’m the guy on the other end of the phone when that question hits. I run a small, no-BS carriage bolt supply shop, so I field this exact query at least three times a week: Are 0 carriage bolts available in different head thicknesses? 0Carriage Bolts
First off, let’s cut through the jargon, because “0 carriage bolt” doesn’t mean it’s a tiny, bolt-sized version of a carriage bolt—though yeah, sometimes folks mix that up (shoutout to the customer last week who asked if we had 0-size bolts for a toy train. No, but I get the confusion). The “0” here is the ANSI (American National Standards Institute) standard number for the shank diameter: 0.5-inch, right? Wait, no—wait, let’s clarify that quick, because specs are where most headaches happen. ANSI B18.5 is the go-to for carriage bolts, and the size number (the 0 in 0 carriage bolt) actually corresponds to the shank’s nominal diameter in sixteenths of an inch. So size 0 is 0/16 = 0.5-inch shank. That’s the standard baseline 0 carriage bolt you’ll see on deck railings, fence posts, heavy-duty furniture frames—stuff that needs to hold solid, not just hang together.
Now, back to the head thickness question. This is way more important than it sounds, by the way. I once had a guy drive 45 minutes to my shop screaming about how his new deck boards split when he tightened his 0 carriage bolts. Turns out he grabbed the first box he found from the big box store, which had thinner heads, and when he cranked the wrench down, the head compressed the soft cedar and split the wood. If he’d had a thicker head, that spread of load would’ve saved him a whole afternoon of repairs and a new 2×6. So yeah, head thickness isn’t a trivial spec—it’s a make-or-break for how well a bolt works.
So, do we (as in, real 0 carriage bolt suppliers, not the big box chains that cut corners) make these with different head thicknesses? Hell yeah, and we’ve been doing it for years—though most people don’t realize that, because standard specs only list one “nominal” thickness, not the variations that exist for specific use cases. Let’s break this down, because there are three main categories of 0 carriage bolt head thickness, and none of them are one-size-fits-all.
First, the standard nominal head thickness, per ANSI B18.5. That’s the baseline for general use. For a size 0 (0.5-inch shank) carriage bolt, ANSI lists the round head thickness as 0.312 inches—about 5/16 of an inch. That’s what you get in the generic boxes at hardware stores, and it works for most casual stuff: like attaching a picket to a fence rail, or hanging a small shelf that holds your toolbox. But here’s the thing: ANSI’s nominal spec is a minimum, right? Wait, no—wait, let me double-check that, because I don’t want to mislead anyone. No, actually, ANSI B18.5 specifies a minimum and maximum for head thickness, not just a single number. For size 0 carriage bolts, the head thickness ranges from 0.290 inches (min) to 0.330 inches (max). Oh, so that’s a range, but is that the “different thicknesses” people are asking about? Kind of, but most of the time when someone emails or calls asking for different head thicknesses, they’re not talking about 0.04 inches of variation in the ANSI range. They’re talking about thicker heads, or thinner heads, that aren’t just within the standard spec.
Which brings me to the second category: heavy-duty extra thick heads. These are the ones for when you’re dealing with higher loads. Think structural work, like attaching a ledger board to your house (the part that holds your deck to the wall—super important, don’t skimp here) or mounting a heavy metal gate that weighs 200+ pounds. For these uses, a thinner standard head will flex or pull through the material over time. So we make size 0 carriage bolts with heads that are 0.375 inches thick—3/8 of an inch. That’s 20% thicker than the ANSI nominal max. The extra thickness means the load is spread over a bigger area, so it doesn’t dig into wood or bend under tension. I had a commercial framer come in last month—he was working on a small public park pavilion—and he needed these thick heads because the deck posts were going to hold picnic tables and playground equipment. He told me a big box supplier sold him regular 0 bolts that bent halfway through the job, so he came to me for the thicker ones. I’ve also got a buddy who builds horse barns—he swears by the thick head 0 carriage bolts for attaching stall doors, because a spooked horse can slam a door hard enough to shear a thin-head bolt. That’s not a story I take lightly.
Then there’s the third category: thin profile heads. Wait, who needs a thinner carriage bolt head, right? I thought that too, until a customer brought me a photo of his new backyard gate. He’d used standard 0 carriage bolts, but the gate frame had a recessed notch for the bolt head, and the standard 0.312-inch head was too tall—so when he closed the gate, it wouldn’t latch. Turns out, thin heads are super useful for flush-mount applications where you don’t want the bolt head sticking out or catching on things. For size 0 carriage bolts, we make thin heads that are 0.250 inches thick—1/4 of an inch. That’s almost a full 0.06 inches thinner than the minimum ANSI spec. The catch here is that you can’t use these for high-load stuff, obviously—they’re for light to medium use, like the gate latch, or attaching a decorative trim to a bookshelf, or any project where clearance is tight. I actually keep a small bin of these thin heads in my shop for exactly that scenario, because I can’t tell you how many times a customer has come in panicking because their custom woodworking project has a hidden groove that standard heads don’t fit.
Now, let’s talk about why you don’t hear about this stuff at your local big box store. It’s simple: they stock the lowest common denominator—standard thickness, lowest cost, and they move enough of them that they don’t need to carry variations. We’re a small supplier, so we cater to the people who actually need specifics. But wait, is there a catch to getting different head thicknesses for 0 carriage bolts? Yeah, sort of. First, availability. The thin and extra thick heads aren’t sitting on a shelf next to the generic 0 bolts—we don’t mass produce them, because not everyone needs them. So you’ve got to order them in advance, usually with a small lead time, unless we have leftover stock from a recent job. Second, material. Wait, some people ask if the thickness is different because of the material—like, can you get stainless steel 0 carriage bolts with different head thicknesses? Absolutely. Same with hot-dip galvanized, plain carbon steel, even silicon bronze for outdoor marine projects. The thickness spec is separate from the material spec, so you can mix and match. Just make sure you specify both when you order: size 0, material, and head thickness, so you don’t end up with the wrong thing.
Wait, let’s address a common myth here. Some folks think that “different head thicknesses” just means a longer or shorter bolt, but no—carriage bolts have a fixed shank length for each diameter, right? So a size 0 carriage bolt is available in lengths from, like, 1 inch up to 12 inches, but the head stays the same diameter (usually 0.75 inches for size 0) and the thickness is the variable. That’s another thing I see people mix up: they’ll say “I need a thicker bolt” and they mean longer, but no—thickness is the height of the round head, not how long the shank is. Important distinction.
I should also mention that not all suppliers do this. A lot of the big bolt distributors only carry the standard nominal thickness for size 0 carriage bolts, because it’s cheaper to stock one SKU instead of three. That’s why I started offering the variations—after that deck repair customer a few years back, I realized most builders don’t know that head thickness is a variable, not a fixed spec. I started carrying the extra thick heads first, then added the thin ones after that gate customer story. Now it’s one of our most popular custom requests.
Another thing: testing. How do we make sure the extra thick heads are actually strong enough? We send samples to a local materials lab to test shear and tensile strength, because we don’t want to sell something that will fail. The thin heads, obviously, aren’t rated for heavy loads, but we test those too just to make sure they don’t snap when you tighten a wrench. We use the same high-quality steel for all our 0 carriage bolts—no cheap, brittle steel that bends or snaps the second you look at it.
Let me wrap this up with a real example to drive the point home. Last spring, I had a customer who was building a custom birdhouse? No, wait, a tiny cabin for his kids in the backyard—like, 10×12, with a cedar floor and pine walls. He used standard 0 carriage bolts for the floor joists, but when he tightened the last one, the head pulled through the soft cedar. He came to me at 6pm on a Friday, panicking, because he had to get the cabin done for his kid’s birthday party the next day. I had a bin of extra thick head 0 carriage bolts in stock, so he ran them to his place, replaced the bad bolts, and got the cabin finished just in time. He left me a $20 tip and a bag of homemade chocolate chip cookies. That’s the stuff that makes this job worth it—when you don’t just sell a bolt, you solve a problem.
So to circle back to the original question: Are 0 carriage bolts available in different head thicknesses? The short answer is hell yes, but most people don’t know that because they’re only buying generic bolts from big stores. The long answer is that there are three main thicknesses: standard nominal (for general use), extra thick (for high-load structural or heavy hardware jobs), and thin profile (for tight clearance or flush-mount projects). You just need to work with a supplier that actually carries these variations, not just the one-size-fits-all garbage.
If you’re working on a project right now and you’re not sure which head thickness you need—whether it’s a deck, fence, gate, custom furniture, whatever—hit me up. I can walk you through it, no pressure. I’ve spent enough time around bolts to know exactly what works for what, and I won’t sell you something you don’t need. Just reach out to connect, and we can chat through your specs. No high-pressure sales, no confusing jargon, just straight answers about carriage bolts.
Wait, one last thing: if you’re ordering, make sure you’re not mixing up shank size. Sometimes folks call a 0 carriage bolt a “1/2-inch bolt” because that’s the shank diameter, which is correct, but I always remind people to confirm the length too—because a 1-inch bolt is way different than a 6-inch bolt. And if you have a super specific project, just send me the details, and I’ll tell you if we have exactly what you need, or if we can get it in for you.
Hex Bolts References:
- American National Standards Institute (ANSI). B18.5-2021: Fasteners, Bolts, Carriage, Square and Hex Heads (Regular, Short, and Long lengths), and Carriage Bolt and Nut Assembly. ANSI, 2021.
- Fabricators & Manufacturers Association International. Fastener Selection Guide for Structural and General Fabrication Projects. FMA, 2022.
- ASTM International. Standard Specification for Steel Carriage Bolts, 150 ksi Minimum Tensile Strength. ASTM A307/A307M-21, 2021.
Ningbo Taida Fastener Manufacture Co., Ltd.
Ningbo Taida Fastener Manufacture Co., Ltd. is well-known as one of the leading 0carriage bolts manufacturers and suppliers in China. Please feel free to buy high quality 0carriage 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/
