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I bought M5 bolts with barrel nut a year ago. Then I bought new M5 bolts a few days ago to replace the old ones. The new bolts do not seem to enter the barrel nuts. Upon closer inspection it seems that the thread on the two is not matching.

When I look for bolts I get size like M5x70mm. But it never says anything about the thread size in the description. Are all M5 bolts supposed to have the same thread size?

FreeMan
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quantum231
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  • The table shows that the thread pitch could be 0.8mm or 0.5mm? This means these are the only two possibilities right? – quantum231 Dec 19 '23 at 01:46
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    That or you are using the wrong size bolt. Title mentions M6, question has M5, hard to tell by sight alone. – crip659 Dec 19 '23 at 02:00
  • I don't have deep experience with metric, but I think that there are only 2 major thread pitches. Maybe somebody else here can weigh in. – Aloysius Defenestrate Dec 19 '23 at 03:53
  • See https://diy.stackexchange.com/a/215225/18078 – Ecnerwal Dec 19 '23 at 12:29
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    @AloysiusDefenestrate realistically there's only one - coarse. I come across fine (and finer) threads in very specific applications in work, but never for simple fastening asks or in consumer products – Chris H Dec 19 '23 at 13:21
  • OK, so based on the answers, it seems that there are 2 thread sizes in the world for M5. I believe that I got M5 the first time around but I could not find the email containing the order details. Based on the measurement from vernier caliper, I concluded that it is M5. – quantum231 Dec 19 '23 at 19:30

2 Answers2

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Metric, like SAE, describe bolts and nuts in form of base diameter x thread pitch.

For M5 nuts/bolts, there are 2 main pitches, .5 and .8 mm. With the .8 being most common by far. The pitch in metric is the actual space between threads, while with SAE, it is expressed as number of threads in 1 inch.

With all that being said, almost every hardware store will have a sizer board where you can get the exact sizes of your bolt or nut.

FreeMan
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Keith
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While metric fine threads exist, you won't find them in furniture. Even in industrial quantities they're far more expensive and reserved for special purposes.

It's much more likely than one of your screws isn't M5. 10-32 UNC is very close, and more common in consumer goods than metric fine, even in metric countries because of legacy designs and international markets. M6 could be confused with M5 if you're not familiar with them, and is very common on furniture fixings. M6 is also close to 1/4-20 UNC.

Chris H
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  • The lesson I learnt is, ALWAYS buy more screws that you need right now and ALWAYS keep copy of the receipt so it is clear what the size is. – quantum231 Dec 19 '23 at 19:31
  • @quantum231 I tend to get mine online, which helps with record-keeping. Bigger bags work out cheaper per screw but it doesn't save much once word gets out that you're well-stocked - not that I mind. I've also got vernier calipers and a thread gauge – Chris H Dec 19 '23 at 20:05
  • There is such a thing as a "thread gauge"? I did not know that. – quantum231 Dec 19 '23 at 20:42
  • @quantum231 yes, it's sky useful for measuring thread pitch, and not even expensive. Of course if you have a known thread you can check the pitch of an unknown thread against it by holding them together with the light behind to see whether they stay in phase – Chris H Dec 20 '23 at 06:28