Metric Bolt size ??

castaway

castaway

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If I get a measurement of 9.42mm across the shank of a bolt (on my digital vernier) does that mean that it is an M9 or M10 bolt ?

I expected to get an exact reading of 9mm or 10mm.

Thanks Nick
 
Agree with above.. But metric threads are often rolled as opposed to being cut so can be larger than the shank ... Measure the OD of the thread

M10 has a pitch of 1.5mm 9mm 1.25 mm but M9 is not a common size

An M10 bolt should have a head which is 17mm AF ( no info for M9)

3/8" UNF has a pitch of 24 tpi and 3/8" UNC 16 tpi

3/8" BSF is 20 tpi and 3/8 Whitworth is 16 tpi
 
Ahhh (groan)...I was wondering if that was the case. These are the mounting bolts of an Australian self steering gear manufactured in the US.

Reason was that I need to buy some Tophat Isolators and these come in either M8 or M10 so it looks like I get the M8 and drill out or M10 and have a slightly sloppy fit.

Thanks everyone (as usual!)

Nick
 
castaway said:
Ahhh (groan)...
Click to expand...

If its american made its unlikely to have metric threads They haven heard of millimetres and all that stuff . Inches, feet, pints and gallons over there ( and not even proper gallons at that!)

On the other hand the Australians are metricated I believe.
 
3/8" is 9.53mm, so a reading of 9.42 would tell me this is a 3/8 thread.

As someone else has already suggested, measure the diameter of the thread not the shank.

An M10 will more than likely read 9.85mm-9.9 mm (on the thread)
The pitch is also important, and someone has already given you the T.P.I (threads per inch) of the imperial sizes.

My suggestion, with the absence of thread guage is to try and carefully measure the between 2 peaks of the thread to determine the pitch.

If it's UNF (24 TPI) the pitch will be as close to 1 mm. It's actually 1.058mm.

If it's UNC (16 TPI) the pitch will be around 1.6 mm. (actually 1.59)

The way I worked this out is as follows 1 divided by 24 (TPI) =.04166

.04166 is the pitch in imperial multltiply this by 25.4 = 1.058mm

Regrds

Colin
 
If the Americans ..

If the Americans had anything to do with it its going to be imperial of some sort . Old Bike Shop might help they usually have a range of bolts and NUTS from around the world :rolleyes:
 
IAN13 said:
If the Americans had anything to do with it its going to be imperial of some sort . Old Bike Shop might help they usually have a range of bolts and NUTS from around the world :rolleyes:
Click to expand...



Yes the Americans not only still embrace Imperial engineering, but still have a number of home grown threads - take for example he standard thread for an antenna mount 1" x 20 tpi. The catch with a bike shop is that they probably won't have much in stainless. Still, nothing lost as you're looking to re-use the originals.

How many top hats do you need? It might be worth turning a few from nylon rod, or maybe you can blag a few from the original manufacturer.

Rob.
 
VicS said:
If its american made its unlikely to have metric threads They haven heard of millimetres and all that stuff . Inches, feet, pints and gallons over there ( and not even proper gallons at that!)

On the other hand the Australians are metricated I believe.
Click to expand...
When I was working in the oil field in the early 80s we eventually had Chevy Silverado pickups shipped to us. They had a mixture of metric and unified bolts on them. By the early nineties they were mostly metric. I suspect that now they are all metric.
Stu
 
VicS said:
If its american made its unlikely to have metric threads They haven heard of millimetres and all that stuff . Inches, feet, pints and gallons over there ( and not even proper gallons at that!)
QUOTE]

I was told many years ago that the USA went metric around 1880, they passed the Bill, but never round to implementing it.

M10 bush would be okay for 3/8", you will not see any real differance.

It could be a thread roll 3/8", when I was a apprentice at Rubery Owen in the 1960's, we made a few million a week.

Brian
Click to expand...
 
Pain isn't it when things are part metric part imperial

many years ago I had a car that was like that. Part Britsh made Vauxhall and part German made Opel.
 
halcyon said:
I was told many years ago that the USA went metric around 1880, they passed the Bill, but never round to implementing it.
Click to expand...

Didn't know that and it seems it has some foundation. This from Wiki:

In the early 19th century, the U.S. Coast and Geodetic Survey (the government's surveying and map-making agency) used meter and kilogram standards brought from France. In 1866, Congress authorized the use of the metric system and supplied each state with a set of standard metric weights and measures.

In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Metre Convention or the Treaty of the Meter. The signing of this international agreement concluded five years of meetings in which the metric system was reformulated, refining the accuracy of its standards. The Treaty of the Meter established the Bureau international des poids et mesures (BIPM, International Bureau of Weights and Measures) in Sèvres, France, to provide standards of measurement for worldwide use.

Under the Mendenhall Order in 1893, metric standards, developed through international cooperation under the auspices of BIPM, were adopted as the fundamental standards for length and mass in the United States. The U.S. customary units such as the foot and pound have been defined in relation to metric units ever since.

The 1895 Constitution of Utah, in Article X, Section 11, originally mandated that: "The Metric System shall be taught in the public schools of the State." This section was, however, later repealed.
 
To OP: you think you've got problems with your 3/8 bolt? Check this out (Wiki, again):

The use of two different unit systems was the cause of the loss of the Mars Climate Orbiter in 1998. NASA specified metric units in the contract. NASA and other organizations applied metric units in their work, but one subcontractor, Lockheed Martin, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit Mars at about 150 kilometers (93 mi) altitude, but incorrect data probably caused it to descend instead to about 57 kilometers (35 mi), burning up in the Martian atmosphere.
 
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