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Appendix
Appendix
Installation & Maintenance
Assemblies
Equipment & Accessories
Fittings
Hoses
Fitting Identification
Fitting Standards
There are five basic fitting standards. They are identified
as North American, British, French, German and Japanese.
North American Thread Types
Also known as American Dryseal Pipe Threads, the
thread types include NPTF, NPSF and NPSM.
N
–
National
S
–
Straight Thread
F
–
Fuels
P
–
Pipe
T
–
Tapered Thread
M
–
Mechanical Joint
Pipe threads can be either straight or tapered. The first
step in identifying this fitting is to determine if the thread
is parallel (straight) or tapered.
A straight thread is not used for sealing fluids. In this
type of fitting, a seal is achieved with an O-ring, a
metal seal, or a seat machined into the end of the
fitting. A straight thread can be determined by laying a
straightedge against the threads. If all the threads are
parallel to the centerline of the fitting, then it is a straight
thread.
A tapered thread seals by the interference in the
engagement of the male and female threads. These
threads deform when they are tightened, causing metal
deformation and a pressure-tight joint. Thread sealants
are commonly used in this connection. A tapered thread
can be determined by laying a straightedge against
the threads. If the straightedge is not parallel to the
centerline of the fitting and the threads taper towards
the centerline of the fitting, then it is a tapered thread.
A fitting may also be referred to by its Dash number. The
Dash number is a universal abbreviation for sizing pipe
systems. The following charts will show a Dash number
for each fitting. The Dash number comes from the
dimension of the port of the fitting. It is the dimension in
1/16
of an inch. A 3/8” port would be 6/16” or a Dash 6 (–6).
Parallel Threads
Tapered Threads
Male
Female
NPTF
Identification
National Pipe Tapered Fuels. Tapered thread.
Seal
The thread is tapered and sealing takes place with the
deformation of the threads. The NPTF male has a
30-
degree seat and will mate with the NPTF female, also
with tapered threads, but no seat. A thread sealant is
commonly used. An NPTF male with 30-degree seat will
mate with an NPSM female, which has straight threads
and a 30-degree inverted seat. The sealing takes place
on the 30-degree seat.
Application
The NPTF fitting is a dryseal thread, commonly used
in fluid power systems but not recommended by
the National Fluid Power Association for hydraulic
applications.
Inch
1/16
SAP #
1/8
2/16
-2
1/4
4/16
-4
3/8
6/16
-6
1/2
8/16
-8
3/4
12/16
-12
1
16/16
-16
1
e
20/16
-20
1
f
24/16
-24
2
32/16
-32