M measurement in Bentley's manual...

I've just noticed that all the nut measurement in the Bentley's manual are some bizzare sizes...For example, the self locking nuts that holds the strut towers and the shock mounts are 13mm metric sized, but the manual lists them as M8 nuts. Also, the 17mm nuts that holds the swaybars are listed as M10 nuts.

Anyone have any idea how these units convert into Metric measurement?

You always spec a nut by it's thread, not the size of tool used to work with it... So in this case, the M8 is an 8mm thread and the M10 is a 10mm thread.

In American measurements a 5/16" nut uses a 1/2" wrench... (that's the closes equivalent to your metric M8 / 13mm example)

If I am not confused, there is a table somewhere way at the beginning of the Bentley which tells you about the M sizing.

Originally posted by Raffi
If I am not confused, there is a table somewhere way at the beginning of the Bentley which tells you about the M sizing.

Damn. Got ownzed.

Thanks doode.

Originally posted by The HACK


Got ownzed.

Huh???

Originally posted by The HACK
I've just noticed that all the nut measurement in the Bentley's manual are some bizzare sizes...For example, the self locking nuts that holds the strut towers and the shock mounts are 13mm metric sized, but the manual lists them as M8 nuts. Also, the 17mm nuts that holds the swaybars are listed as M10 nuts.

Anyone have any idea how these units convert into Metric measurement?

The "M" system is actually quite common, but HACKs such as myself or yourself find it just confusing. I prefer the shadetree system of just naming a bolt after the size socket you need to fasten it. Of course, that has nothing whatsoever with the M, which measures thread size IIRC. Well, so it does have something to do with it, but it doesn't...well, but...ugh. never mind.





0wN3d.

The problem with head size is that the head could be a different size but the bolt could still thread properly. I believe the M system dictates what thread goes with what head size.

I hate how with standard SAE stuff you could easily have 2 bolts with the same head size have totally different thread pitches and make it easy to strip threads.

Originally posted by Kaz
The problem with head size is that the head could be a different size but the bolt could still thread properly. I believe the M system dictates what thread goes with what head size.

I hate how with standard SAE stuff you could easily have 2 bolts with the same head size have totally different thread pitches and make it easy to strip threads.

Yup. The M system is undoubtedly better, it's just not as easily intuitive as the plain old "socket size = bolt size" system. I gotta sit down and commit the M to memory one day, not that it would take that long.

The M just means Metric.

US sized bolts are also sized by shank or thread size.

If you go to the hardware store and buy 1/4 bolts, the threaded portion will be 1/4 diameter. The head take a larger sized wrench.

There are standards for head size to bolt size in US, but we have LOTS of different "standards".

What you normally get at the hardware store is SAE Coarse thread.

There is also SAE Fine thread. And AN (Army/Navy used in aircraft), and don't forget Whitworth on old Brit cars and bikes (the wrench sizes are even different), and ...

To properly spec a bolt you should use diameter, thread pitch and standard. So you typically buy a 1/4" x 20 bolt at the hardware store, which means 20 runs per inch of thread.

IIRC metric bolts used to be speced the same way, with a diameter and the thread spacing in mm. But the M defines a single thread pitch for each diameter.

Originally posted by Pinecone
and don't forget Whitworth on old Brit cars and bikes (the wrench sizes are even different), and ...

....

IIRC metric bolts used to be speced the same way, with a diameter and the thread spacing in mm. But the M defines a single thread pitch for each diameter.

ACK! Whitworth! There is something wrong with a system

If a bolt is specified with only an Mx where x is the nominal diameter, the the thread pitch is the standard pitch. You can specify a non-standard pitch by adding the pitch to the nominal diameter:
M12 = M12X1.75
M12x1.5

Even for metric fasteners, the head size is not necessarily dictated by the thread. There are standards but auto manufacturers love special fasteners.


Ed