Bolt size is measured from the end of the threads to the bottom of the
bolt head. The bolt head diameter makes no difference in general
measurements.
When threads are cut or rolled the outside diameter will be reduced a
bit. So a 5mm bolt will have a thread diameter measurement of
something like 4.9mm.
Bolt Size Measurements
The example to the left shows an M5x20.
When measuring a countersunk bolt it is always
measured by the TOTAL bolt length.

In the example 20mm includes the head height.

Items like Thomson seat post bolts are also
measured like this because the bottom of the head
has a chamber. This can be seen in the example
below.
Here is a list of common thread pitches in my store:
Pitch means how fine or coarse the actual threads are.
All bolts are these pitches unless otherwise specified.
M3=0.5
M4=0.7
M5=0.8
M6=1.0
M7=1.0
M8=1.25
M10=1.5

10mm bolts are common to use 1.25 pitch.
For this type of pitch a 1.25 pitch bolt will have finer
threads than 1.50 pitch.
Crank bolts are 1.0 pitch
A finer pitch bolt or nut will be stronger as there is more
contact with metal on the threads.
The socket the bolt uses does not determine the bolt size!
This is really important and a common mistake made.
You measure the diameter of the shaft to come up with the "M5" value.
For example a M5x10 bolt has a 5mm shaft diameter and is 10mm long from
the bottom of the head to the end of the fastener.

There is no other way to measure a bolt. If a bolt or screw uses a hex socket
or a screwdriver then there is no other possible way.
The Bolt Size Measuring Exception is Countersunk Bolts
Bolt Thread Pitch
To make a proper measurement you need a caliper or
something to reference.

The bicycle world uses some common bolts to give you
an idea and then can compare to other fasteners.

Places that use 4mm bolts:
Those little screws the make tension for derailleurs.

Places that use 5mm bolts:
Water Bottle cage, Disc brake rotor bolts (Usually torx),
Thomson Seatpost Bolts. Dura Ace Pad, Derailleur cable.

Places that use 6mm Bolts:
Caliper Mounts, Headset Top Caps.
Common Bolt Size Measurements
Road Chainring Bolt and Nuts for "Singles"
MTB Chainring Bolt and Nuts for "Doubles"
Measuring Hex Nut Size
The titanium hex nut
above is 6mm.
The hex is = 10mm
The Flange is = 14mm
If you measure wrong you will need to return for a refund and re-order.
Shipping charges will apply and are not refundable.
Torquing non-steel Bolts - Torque Wrenches
Torque of Titanium and Aluminum is not the same as Steel
This is really important and a common mistake made.
I don`t use a torque wrench on most bolts. With the proper tool I can feel how
tight the bolt gets. After time this becomes intuitive.
Titanium should be about 80% the torque of steel
Aluminum should be 50-60%

Ti-prep should be used with titanium.

Hope our Measuring Bolts page helps To Measure Bolts
Titanium is about 1/2 the weight of steel.
Aluminium is 1/3 the weight of steel.

Titanium has several advantages over steel. Most importantly is corrosion
resistance and the weight is reduced in half. Strength is about the same but
caution should be used when tightening that the socket won't strip.
Titanium can also be polished to close to mirror reflection.

Aluminum is much lighter and also has corrosion resistance if anodized.
Aluminum that is not anodized can be polished to a mirror like finish.
Strength is reduced and one should be careful when torquing.
Also Aluminum has a bit of memory loss so once a bolt is tightened and
then loosened it will loose a bit of strength when re-tightened.  This seems
to be a common cause of frame failure on aluminum frames over time.
Weights of Metals
How to measure bolt size?
Below I have been posting
more detail on bolt measurement.
The Green Thomson Bolts are also considered countersunk.
See the bottom of the head? It has a chamfer.
Measurement of metric bolt should always be done with metric. 5mm, 6mm,
ect. Imperial bolt sizes will use fractional and the measurements don't carry
over easily at all. If you ask for a 6mm bolt that is 1.25" long the calculation
will have to be preformed and is most confusing in ordering.
Metric Bolt Size VS. USA Size
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From Canada is Costly and
Extra Charges Apply
All Prices are in US Dollar
$5.00 Shipping via Air Mail.
Overseas is $10.00
Tracking is extra Costs!
Bolt Size, How to Measure a Bolt, Measure a Metric Bolt
Titanium Fasteners Metric, Titanium Fasteners Specs
Please measure before you order to make sure you have the correct item. There are
many varations in this business. We do not refund for mis-measured items.
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