Page 74 - FittingsCatalog

MISCELLANEOUS INFORMATION
Copyright © 2002-2007 74 BrakeQuip
Worldwide there are only two
measuring systems – Metric and
Imperial. Some times the imperial
measurement is called SAE or
American.
Metric systems measure the thread by
the distance between two thread
pitches expressed in millimeters.
Example: M10 x 1 = The OD of the
thread is 10mm and the distance
between each thread pitch is 1mm.
Imperial systems measure the number
of thread pitches over a one inch
length.
Example: 7/16 x 24NS = The OD of
the thread is 7/16 and the number of
thread pitches over a one inch length
is 24.
After some experience of looking at
threads a lot and knowing what
vehicle the fitting came from, you will
be able to determine fitting threads by
just looking at them.
Determining if the thread is metric
or imperial.
The easiest way is using a thread gauge.
BrakeQuip offers a thread
identification kit (BQ2100) for this
purpose and covers the majority of
threads that you will encounter
working with brake plumbing.
Another method could be to use a
brake hose fitting or tube nut from
your stock that you can confirm the
thread and size from.
If this fails do the following;
1. Determining the fitting OD
(a) If a male fitting – Measure the
OD of the thread. Take into
account that this measurement
will be slightly under the nominal
size. The one size that may trick
you up here is 7/16". This will
probably measure 11mm. This
size is extremely rare so it will
probably be the most common
7/16" size which is 7/16" x 24NS.
(b)If a female fitting – Measure the
ID of the thread. Compare this
measurement at the distance
between the “valleys” of opposing
pitches with corresponding male
fittings.
2. Determining the thread pitch
If it is an imperial size – Count
the number of thread pitches
over say 1/2" length and then
multiply by 2 to get your T.P.I
(Threads per Inch)
If is an metric size – Measure the
distance between two thread pitches to
determine the thread pitch.
Imperial Threads found on braking
systems
3/8 x 24NF 7/16 x 24NS 9/16 x 20NS
3/8 x 20BSF 1/2 x 20NF
7/16 x 20NF 9/16 x 18NF
Metric Threads found on braking
systems
M9 x 1 M10 x 1.5 M12 x 1.25
M10 x 1 M11 x 1.25 M12 x 1.5
M10 x 1.25 M12 x 1 M14 x 1.5
Abbreviations
NF = National Fine
NS = National Special
BSF = British Standard Fine
Identifying the Correct Thread
Checking the Thread Type
Male & female threads can be checked using the BrakeQuip Thread Gauge #BQ2100