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Jan 09, 2007, 04:30 AM
Kamikaze Heli Pilot
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M2.6 vs M2.5 threads

Didn't want to hijack Larren's thread on loose screws but I have been looking to buy some taps and dies so this question has come up. Also, a recent communication with Ade made me think.

The ISO standard recommends M2.0 x 0.4, M2.5 x 0.45, M3.0 x 0.5 etc

But, in Japan (Futaba, JR, Hirobo, Kyosho, Quick, O.S., Y.S. etc etc) they follow a slightly different set of standard sizes, M2.0 x 0.4, M2.6 x 0.45, M3.0 x 0.5. I also came across the remarkably stupid M3.5 x 0.6 for the first time in my engineering life while working on a Hirobo muffler. Anyhow, back to the subject - There are several parts that are built using M2.6. For me, living here, even in simple hardware stores, I can buy M2.6 here no problem, but I never see M2.5

For anyone outside Japan / Asia I guess the situation is not so simple. While it seems to be possible to get M2.6 via the internet, M2.5 definitely seems to be more common and I guess it could be easy to mistakenly use an M2.5 screw in an M2.6 hole.

I know it's only 0.1 mm but on this size of thread, the thread height is only 0.28mm so fitting an M2.5 screw in an M2.6 hole could really ruin your day.

I just wondered if anyone has experienced any problems on this such as stripped threads, screws coming loose etc.
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Sep 16, 2013, 06:59 PM
FNFAL's Avatar
Indeed, a M2.6 screw will only go so far in a M2.5 hole until binding will occur. You can force it, but not a good idea. Strange to have thread specs so close yet different.

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