{"id":473,"date":"2026-09-28T22:50:09","date_gmt":"2026-09-28T14:50:09","guid":{"rendered":"http:\/\/www.kurunews.com\/blog\/?p=473"},"modified":"2026-09-28T22:50:09","modified_gmt":"2026-09-28T14:50:09","slug":"are-0-carriage-bolts-suitable-for-high-temperature-environments-47ec-155706","status":"publish","type":"post","link":"http:\/\/www.kurunews.com\/blog\/2026\/09\/28\/are-0-carriage-bolts-suitable-for-high-temperature-environments-47ec-155706\/","title":{"rendered":"Are 0 Carriage Bolts suitable for high – temperature environments?"},"content":{"rendered":"

Hey everyone, it\u2019s Jake here from the carriage bolt supply team \u2013 and before you ask, yeah, I\u2019m the same guy who posts dumb bolt fail reels on our company Instagram (don\u2019t @ me, my boss still doesn\u2019t get the joke). Today we\u2019re tackling a question I get at least twice a week on calls: \u201cAre 0 carriage bolts suitable for high-temp environments?\u201d 0Carriage Bolts<\/a><\/p>\n

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First off, let\u2019s cut the crap \u2013 when people say \u201chigh temp,\u201d they mean different things. For a backyard deck builder it\u2019s 150\u00b0F and blistering, for a refinery tech it\u2019s 800\u00b0F and explosive fumes, and for a foundry worker? Let\u2019s just say that bolt\u2019s gonna glow orange before the day\u2019s out. Most of the time I get this question, folks are mixing up \u201chigh temp\u201d with \u201cmy specific job\u2019s high temp,\u201d so let\u2019s break this down like I explain it to my cousin who thought 316 stainless was a coffee mug material (true story).<\/p>\n

First, let\u2019s clarify what \u201c0 carriage bolts\u201d actually are \u2013 yeah, that\u2019s the head size, right? Wait, no, hold up, for anyone new: when we say \u201c0 carriage bolts,\u201d we\u2019re talking about the size designation for the head\u2019s width, not the shaft. Carriage bolts have that round, domed head with a square shank under it, right? The square part stops it from spinning when you tighten the nut, which is why they\u2019re used for things like fence rails, trailer frames, heavy equipment brackets, and sometimes even HVAC ductwork that\u2019s near furnaces. The \u201c0\u201d is just the ANSI (American National Standards Institute) size that translates to a 1\/2-inch nominal shaft diameter, for anyone who wants the nerd version. Good, now we\u2019re on the same page.<\/p>\n

Now, the big question: high temps. Let\u2019s start with what 0 carriage bolts are typically made of, because that\u2019s 90% of the answer. Most standard 0 carriage bolts \u2013 the ones that go to your local hardware store or big box \u2013 are made of plain carbon steel, maybe a cheap zinc-plated coating for rust resistance. Here\u2019s the thing about plain carbon steel: it melts at around 2750\u00b0F, but it starts to lose its structural strength way before that. At 400\u00b0F, carbon steel is about 90% as strong as it is at room temp. At 600\u00b0F? We\u2019re down to 75%. By 800\u00b0F? It\u2019s half its original strength. And if you throw constant thermal cycling \u2013 like a part that goes from room temp to 500\u00b0F every hour, expanding and contracting \u2013 you get metal fatigue way faster. So standard plain steel 0 carriage bolts? Definitely not for anything over 500\u00b0F, and even then, only if the cycle is super mild. I\u2019ve seen guys install these on a small water heater manifold that runs at 450\u00b0F, and they lasted 3 years. Install the same ones on a stack that hits 700\u00b0F every day for a refinery pump? They snapped in 3 months. Not fun.<\/p>\n

But wait \u2013 we don\u2019t just sell plain steel, right? That\u2019s why I get the second call: \u201cWhat if I get the upgraded ones?\u201d Yeah, we stock coated and alloyed 0 carriage bolts for exactly this reason. Let\u2019s talk about common upgrades. First, hot-dip galvanized (HDG) carbon steel. The zinc coating helps with rust, but what does it do for temp? Zinc melts at 787\u00b0F, so the coating is gone before you hit 800\u00b0F. Under that, though, the carbon steel core is still there \u2013 but same strength curve applies. HDG 0 carriage bolts are fine up to 550\u00b0F, but not beyond. They\u2019re good for outdoor stuff near grills or patio heaters, but not for industrial high-temp.<\/p>\n

Next, stainless steel. This is where things get tricky, because not all stainless is equal for high temps. The most common stainless for bolts is 304, right? What\u2019s its temp rating? Room temp strength is a given, at 800\u00b0F it\u2019s around 85% as strong as 304 at room temp, and it\u2019s got good corrosion resistance. But if you go above 1000\u00b0F? 304 starts to \u201csensitize\u201d \u2013 that means the chromium in the steel reacts with carbon to form chromium carbides at the grain boundaries, which makes it super prone to corrosion (like rust holes) and weakens it. So 304 0 carriage bolts are good up to 1000\u00b0F, but only if it\u2019s a constant temp, not cycling. If it cycles, the fatigue hits hard at 900\u00b0F.<\/p>\n

Then there\u2019s 316 stainless, which people think is better. It is \u2013 a little. It has molybdenum, so better corrosion resistance, but its high-temp strength is almost identical to 304 up to 1200\u00b0F. The big upgrade for high temps is 304H or 316H stainless steel \u2013 the \u201cH\u201d stands for \u201chigh carbon.\u201d Wait, why does carbon matter here? Because at high temps, you want the steel to maintain its structure, and the higher carbon content makes it more resistant to that sensitization we talked about. 304H 0 carriage bolts can handle constant temps up to 1500\u00b0F, and even 1700\u00b0F if the cycle is slow (like once a day, not every hour). I had a customer last year who used these for a kiln\u2019s access door \u2013 runs at 1450\u00b0F nonstop, and his bolts have been going strong for 18 months, no issues. Compare that to when he tried 304, which lasted 2 months.<\/p>\n

But wait, there\u2019s more. What if you\u2019re going even higher? Like, 2000\u00b0F? Stainless won\u2019t cut it \u2013 it starts to soften big time above 1500\u00b0F. For that, we use alloy steel bolts, specifically ones made with materials like Inconel or high-temperature carbon alloys. We carry Inconel 625 0 carriage bolts, which are basically heat-resistant superalloys. They can handle constant temps up to 2000\u00b0F, and even up to 2200\u00b0F for short periods. The downside? They\u2019re way more expensive than standard bolts, and they\u2019re harder to work with because they don\u2019t thread as easily. But for applications like furnace flanges, foundry conveyors, or boiler supports where temps are consistently over 1500\u00b0F, they\u2019re the only game in town with 0 carriage bolt size.<\/p>\n

Now, let\u2019s talk about common mistakes we see customers make all the time. First, guessing. I had a guy last month who bought standard 0 carriage bolts for a smoke stack that hits 900\u00b0F, because he \u201cheard stainless works.\u201d It was 304, lasted 3 weeks. He tried to blame us, but when we looked at his specs, he never told us it was a smoke stack, not a fence. Second, ignoring thermal expansion. Different metals expand at different rates. If you bolt a steel carriage bolt to a cast iron part that\u2019s heating up, they expand at different speeds \u2013 that can cause the bolt to seize or snap, even if the temp is within the bolt\u2019s rating. Third, forgetting about atmosphere. If your high-temp environment has moisture, sulfur, or other corrosive gases, that changes everything. A bolt that\u2019s fine in a dry 1500\u00b0F kiln might corrode in 1000\u00b0F flue gas with sulfur in it.<\/p>\n

Wait, let\u2019s also address a question I get a lot: \u201cCan I just use thread sealant or high-temp grease to make standard bolts work?\u201d No, and here\u2019s why. Grease breaks down at 500\u00b0F max \u2013 above that, it turns to carbon, which is just as bad as no lubricant when you\u2019re tightening a bolt. Thread sealant? High-temp silicone sealant might work up to 500\u00b0F, but anything higher and it burns away, leaving the threads dry. And dry threads when tightening a bolt at high temp? You\u2019ll strip the shank or break the head before you get it to the right torque. Don\u2019t waste your time or money on hacks \u2013 get the right bolt first.<\/p>\n

Now, let\u2019s wrap this up with a quick cheat sheet, \u2018cause I know you\u2019re scrolling and don\u2019t want to read all the nerd stuff again. For 0 carriage bolts in high temp:<\/p>\n