Technical
150
Dixon Fire 2014
US: 877.712.6179 Canada: 800.786.9697 • dixonvalve.com
Technical
P
Identifying Threads
,
dentifying threads can sometimes Ee the most difficult and frustrating part of coupling selection However without the right
comEination of threads you may not provide a functional or safe connection
The diameters threads per inch (TP,) and thread pitch etc are necessary to completely identify a thread 5ing Plug and G2
N2G2 gauges are required to accurately gauge or identify threads ,n the field in the aEsence of these gauges thread leaf
gauges can Ee used to identify the "Threads Per ,nch" (TP,) and the thread pitch 2n threads you have determined to Ee straight
threads a caliper can Ee used to measure the "2utside 'iameter of the 0ale" (2'0) or the ",nside 'iameter of the )emale"
(,'))
$ caliper can also Ee used to taNe measurements of tapered thread diameters However these are more difficult to
define Eecause of the taper )ortunately there are few tapered threads to deal with and these can usually Ee identified from the
nominal 2'0 and the TP,
However identifying the thread may not fully identify what is needed in a mating fitting The application is the primary limiting
factor on the thread type used 'ixon offers products with a wide variety of threads used with hose pipe and hydraulics
:
hen attempting to choose a fitting it is always advisaEle to first identify the thread to which it must connect This may entail
checNing with a fitting or equipment manufacturer
The fire hose thread specifications for some local municipal fire equipment and hydrants may vary according to local
specifications These can generally Ee most easily identified Ey contacting the local fire department responsiEle for the hydrant
The most common thread used on fire equipment is National Standard Thread (NST) also Nnown as National Hose thread (NH)
:
hen it is not possiEle to identify the thread
1)'
etermine the numEer of threads per inch Ey measuring the distance from peaN of thread to peaN of thread
across the largest numEer of whole threads Then divide the numEer of threads Ey the measurement
(
This will provide the TP,)
2)&
hecN to see if the thread is straight or tapered
a)Straight Threads
0
easure the "2utside 'iameter of the 0ale" (2'0) or the ",nside 'iameter of the )emale" (,'))
from peaN of thread to peaN of thread
E)Tapered Threads
0
easure the "2utside 'iameter of the 0ale" (2'0) at the large end and the small end or the
",
nside 'iameter of the )emale" (,')) at the large end and the small end from peaN of thread
to peaN of thread Then measure the 2utside 'iameter (2') of the unthreaded pipe
2
nce the application and these two pieces of information have Eeen determined the thread can generally Ee determined
:
hen in douEt contact the factory
IT IS IMPORTANT TO IDENTIFY THE THREADS REQUIRED BEFORE ORDERING COUPLINGS.
Straight Thread
Tapered Thread