ISO Metric Thread Pitch...
16 January 2009, 10:20 AM
#1
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ISO Metric Thread Pitch...
After an interesting title like that, Im not sure that I can keep your interest up, but..... M8x25 allen cap head bolt, which thread pitch is likely to be the more common? Im guessing that itll be 1.25, but Im not certain and I can only tap the holes the once.
Any help appreciated.
Any help appreciated.
16 January 2009, 10:26 AM
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Can you not find a nut that fits the cap head thread and then run the tap through the nut and see if they are the same, or do you not have the cap heads.
I have just bought a load of M8 cap heads but they are at home with my thread gauge and I'm at work.
I have just bought a load of M8 cap heads but they are at home with my thread gauge and I'm at work.
16 January 2009, 10:29 AM
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After an interesting title like that, Im not sure that I can keep your interest up, but..... M8x25 allen cap head bolt, which thread pitch is likely to be the more common? Im guessing that itll be 1.25, but Im not certain and I can only tap the holes the once.
Any help appreciated.
Any help appreciated.
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16 January 2009, 10:39 AM
#8
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Ive just found the very intersting ISO standard!
Unfortunately there isnt a nut in the equation: Im having to re-tap the captive mounts in the floor of a car. Im going up from M6 10mm headed bolts to M8 cap heads and the more I looked at them the more they looked like a fine thread. Their supplier just shifts boxes of stainless fastners and doesnt have any technical support (but assures me that theyre what everyone uses, which should have looked coarser, I thought).....
All replies appreciated apart from Chris's: 1.25 - coarse itll be then.
Unfortunately there isnt a nut in the equation: Im having to re-tap the captive mounts in the floor of a car. Im going up from M6 10mm headed bolts to M8 cap heads and the more I looked at them the more they looked like a fine thread. Their supplier just shifts boxes of stainless fastners and doesnt have any technical support (but assures me that theyre what everyone uses, which should have looked coarser, I thought).....
All replies appreciated apart from Chris's: 1.25 - coarse itll be then.
16 January 2009, 10:41 AM
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16 January 2009, 02:30 PM
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If you've got a steel rule it's not that dificult to measure the threads on a bolt.
The trick is not to try and measure each individual pitch, but rather watch the progression.
For instance, on the M8 bolt in question, the first peak will be at 0, the second peak will be a bit longer than one, the third about half way between 2 & 3, the fourth at nearly 4, and the fifth will be at 5.
Therefore you have 4 pitches over 5mm giving you a 1.25mm pitch. Depending on the lenght of the thread, you can check it at 10, 15 & 20 mm to be sure of the progression too.
And it's a lot quicker to do than to write
The trick is not to try and measure each individual pitch, but rather watch the progression.
For instance, on the M8 bolt in question, the first peak will be at 0, the second peak will be a bit longer than one, the third about half way between 2 & 3, the fourth at nearly 4, and the fifth will be at 5.
Therefore you have 4 pitches over 5mm giving you a 1.25mm pitch. Depending on the lenght of the thread, you can check it at 10, 15 & 20 mm to be sure of the progression too.
And it's a lot quicker to do than to write
17 January 2009, 11:25 AM
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Just measure 10 pitches Simon.
if it's 12.5mm its 1.25 mm fairly obviously.
It's a bit of a mis-noma saying metric 'coarse'. The coarse threads are always standard. If there is no designation it will always be standard pitch ie if you buy something M8 that does not say 'fine' or 'coarse' it will be 1.25 pitch.
M8 is 1.25 pitch.
M8 fine is 1.0
M8 coarse is 1.5
Standard pitches in common sizes are as follows.
M5 is 0.8
M6 is 1.0
M8 is 1.25
M10 is 1.5
I'm sure you know this, but your minor diameter (i.e the size of drill you need) is Diameter minus pitch, so for a M8 tap you ned a 6.8 drill. For a M8 fine tap you would use a 7.0 drill etc..
if it's 12.5mm its 1.25 mm fairly obviously.
It's a bit of a mis-noma saying metric 'coarse'. The coarse threads are always standard. If there is no designation it will always be standard pitch ie if you buy something M8 that does not say 'fine' or 'coarse' it will be 1.25 pitch.
M8 is 1.25 pitch.
M8 fine is 1.0
M8 coarse is 1.5
Standard pitches in common sizes are as follows.
M5 is 0.8
M6 is 1.0
M8 is 1.25
M10 is 1.5
I'm sure you know this, but your minor diameter (i.e the size of drill you need) is Diameter minus pitch, so for a M8 tap you ned a 6.8 drill. For a M8 fine tap you would use a 7.0 drill etc..
Last edited by p1mark; 17 January 2009 at 11:26 AM.
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