How Fastener Measurements Are Notated
US Fasteners
US Fasteners are described by material,
head style,
and type followed
by or preceded by the diameter
dash thread count (machine threads
only) X length.
The diameter and length are in inches with the exception of
small screws whose diameter may be a size number (ex. 12).
In this case the number will often have a # sign before it
(ex. #12)
Example:
Brass Philips Flat Head Machine Screw 1/4-20 x 6
This is a brass counter sunk (flat head) machine screw with
a Phillips drive. It has a diameter of 1/4 inch, 20 threads
per inch (course thread), a length of 6 inches.
There are some variations on this using abbreviations and
sometimes moving the material and or head style and type to
after the size. For help with abbreviations please see our
Common Fastener Abbreviations
page.
Example:
Philips Flat Head Machine Screw 1/4-20 x 6 Brass
1/4-20 x 6 Brass Philips Flat Head Machine Screw
PFH MS 1/4-20 x 6 BR
BR PFHMS 1/4-20 x 6
Sometimes a machine thread is specified as course thread
or fine thread, rather than giving the actual thread count.
This is usually done with an abbreviation at the end or occasionally
in front of the diameter and length. For help with abbreviations
please see our Common Fastener
Abbreviations page.
Example:
Brass Philips Flat Head Machine Screw 1/4 x 6 CT
For help locating fasteners in our catalog please see How
to Locate Fasteners in our Catalog.
Metric Fasteners
Metric fasteners material,
head style,
and type are
described in a similar manner to US fasteners. However, instead
of threads per inch, the metric system uses thread
pitch (the length of each thread in millimeters measured
along the shaft of the bolt). The thread pitch is written
between the diameter and
length (both measured in
millimeters) and is separated on each side by an X.
Typically the diameter of a metric bolt is preceded by a capital
M to designate metric.
Example:
Class 8.8 Hex Bolt M10 x 1.5 x 20
This is a hex head bolt with a diameter of 10mm, a 1.5 thread
pitch, measuring 20mm long and made of Class (grade) 8.8
steel.
There are some variations on this using abbreviations and
sometimes moving the material and or head style and type to
after the size. For help with abbreviations please see our
Common Fastener Abbreviations
page.
Example:
Hex Bolt M10 x 1.5 x 20 CL 8.8
Note: Metric fasteners may also be specified by DIN number.
The DIN number specifies a particular set of standards that
the bolt adheres to.
For help locating fasteners in our catalog please see How
to Locate Fasteners in our Catalog.
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