Knowledge of the sewing thread
1. Construction and manufacturing process of the sewing thread
Natural textile products such as cotton thread, silk thread, etc. have been used as sewing thread before.
Nowadays, however, chemical fiber products such as polyester thread, nylon thread, etc. are largely used.
Filament thread, spun thread, woolly thread, mono-filament thread, etc. are properly used in accordance with
materials or applications. These threads are different from one another in construction and manufacturing
process as given below.
Filament thread
Filament thread means that left twist (Z twist) is applied to the thread after right twist (S twist) is applied to
the filament (long fiber) that is spun by melting and doubling of 2 to 3 filaments is performed.
Spinning (first twist) Doubling ･ Twist (second twist)
Long fiber that is spun by melting
Single yarn ･ S twist
Triple ply ･ Z twist
<Fig. 㸌-1>
Spun thread (cotton thread, synthetic spun thread)
Spun thread means that left twist (Z twist) (second twist) is applied to the staple (short fiber) after doubling
(first twist) of right twisted single yarn and doubling of 2 to 3 yarns is performed.
Twist (first twist) Doubling ･ twist (second twist)
Short fiber such as cotton and synthetic Single yarn ･ S twist
fiber ( Synthetic fiber means that the Triple ply ･ Z twist
long fiber that is spun by melting is cut
into the short fiber. )
<Fig. 㸌-2>
Wooly thread
Filament yarn is performed the first twist and the twist is returned after superheating setting in the state that
the yarn is strongly pulled.
Wooly thread is a thread that doubling of these two yarns is performed and the twist is applied. This thread is
called filament expansion processed thread.
Untwisting
Single yarn ･ S twist (first twist), heat set
Doubling ･ twist (second twist)
Single yarn ･ Z twist (first twist), heat set
Long fiber that is spun by
Two-plied yarn ･ Z twist
melting
Untwisting
<Fig. 㸌-3>
Monofilament thread
This thread is just the same as long fiber that is spun
by melting and a long yarn without twist.
In addition to sewing thread, this thread is used for
fishing thread or the like. <Fig. 㸌-4>
2. Twist of the sewing thread
Twist of the sewing thread is normally carried out by doubling 2
to 3 yarns and applying left twist (called second twist) to the
yarns after applying right twist (called first twist) of single yarn.
The reason is that return of the twist due to the rotaion of the
hook should be protected and that in case of normal stitching,
the form becomes stable since friction between needle eyelet
and thread is small and return of twist of thread is difficult to
move. On the contrary, when the right twisted thread is used in
normal stitching, friction between needle eyelet and thread is Z (left twist) S (right twist)
large, and the twist is easy to move. Then, the thread loop in
<Fig. 㸌-5>
the state of return of twist is formed, resulting in stitch skipping
or thread breakage.
To distinguish the twist direction, although the right twist is called S twist and the left twist Z twist, when
picking up the thread with thumb and first finger of your right hand, the twist line flowing from upper left to
lower right along the thumb is seen if it is the right twist. On the contrary, when holding it with your left hand,
the twist line flowing from upper right to lower left is seen if it is the left twist.
3. Numbering of the thread thickness
Thread thickness is calculated from the mutual relations between length and weight. The thickness is not
represented by the diameter since the cross section of fiber is not a circle. Therefore, the thickness is
represented from the relations of "length" and "weight". There are "length numbering system" based on the
length and "weight numbering system" based on the weight for the representation.
1) Length numbering system
There are mainly Decitex (dtex) and Denier (D)
-1 Decitex
Decitex is called "1 dtex" when a piece of yarn, weighing 1 gram, is 10,000 meters long, and "2 dtex"
when weighing 2 grams. This numbering is the numbering system for the thickness of sewing thread for
industrial sewing machine to be applied to all threads.
-2 Denier
Denier is called "1 Denier" when a piece of yarn, weighing 1 gram, is 9,000 meters long, and "2 Denier"
when weighing 2 grams.
This numbering is used for silk thread, synthetic filament thread (polyester thread, nylon thread, etc.)
2) Weight numbering system
There are mainly metric number, English number, etc.
-1 Metric number
Metric number is called "Nm 1" when a piece of thread, weighing 1,000 grams, is 1,000 meters long, and
"Nm 2" when the thread is 2,000 meters long. This numbering is used for worsted and woolen yarn.
-2 English number for cotton
English number for cotton is called "Ne 1" when a piece of thread, weighing 1 pound (453.6 g), is 840
(768.1 m) yards long, and "Ne 2" when the thread is 1,680 yards long. The thickness of cotton single yarn
is represented by English numbering. This numbering is used for cotton thread, silk spinning and staple
fiber.
3) Nominal count (thread count)
For "nominal count" (thread count) of the respective filament thread and spinning thread, the nominal count
that can be used in JIS (Japanese Industrial Standard) and the range of total size are normalized. Filament
thread and spinning thread are different in the total size although "nominal count" is the same. So, be
careful.
-1 Conversion table of sewing thread count
Filament <Table 㸌-1>
Nominal Construction Total size of thread used Nominal Construction Total size of thread used
count dtex (D) count dtex (D)
(Thread (Thread
count) count)
#1 3x3 2100 to 2520(1890 to 2250) #40 1x3 300 to 370(270 to 330)
#3 2x3 1750 to 2000(1575 to 1800) #50 1x3 220 to 267(200 to 240)
#5 2x3 1400 to 1700(1260 to 1500) #60 1x3 155 to 190(140 to 170)
#6 2x3 1167 to 1333(1050 to 1200) #80 1x3 117 to 150(105 to 135)
#8 2x3 978 to 1100(880 to 1000) #100 1x3 99 to 112(90 to 100)
#10 2x3 822 to 955(740 to 860) #120 1x2 78 to 90(70 to 80)
#20 2x3 660 to 801(600 to 720) #140 1x2 56 to 66(50 to 60)
#30 1x3 440 to 534(400 to 480) #150 1x2 44 to 50(40 to 45)
* For the indication method of the thickness of sewing thread for industrial sewing machine, indication
of "Decitex" and "Nominal count" is compulsory.
Spinning thread <Table 㸌-2>
Nominal Count of Number Total size Nominal Count of Number Total size
count original of count original of
(Thread thread doubling (Thread thread doubling
count) (dtex) threads count) (dtex) threads
#8 20s(300) 4 1200dtex # 50 50s(120) 3 360dtex
# 20 20s(300) 3 900dtex # 60 60s(100) 3 300dtex
# 30 30s(200) 3 600dtex # 80 80s(74) 3 222dtex
# 40 40s(145) 3 435dtex # 100 64s(92) 2 184dtex
4. Melting point and softening point (ﾟC) of sewing thread
Both points are the indication of thermal resistance. Melting point means the temperature that sewing thread melts by
heat. Softening point means the temperature that the thread starts softening by heat. Especially, in case of synthetic
thread, stitch skipping or thread breakage occurs according to the circumstances. Accordingly, the thermal resistance
is one of the important points. In addition, the thermal resistance affects the temperature setting of iron and press in the
rear process. It is necessary to select a proper sewing thread after considering these factors.
Melting point and softening point of general sewing thread <Table 㸌-3>
Polyester Nylon 6 Nylon 66 Vinilon Cotton
Melting point 255 to 260ﾟC 215 to 220ﾟC 250 to 260ﾟC Unknown Decomposed at
150ﾟC
Softening 238 to 240ﾟC 180ﾟC 230 to 235ﾟC 220 to 230ﾟC None
point
As to the cotton, temperature at which the carbonization starts is described.
5. Strength and ductility of the sewing thread
The force that is required to cut sewing thread by applying a load to the sewing thread in a certain direction
is called "strength". Percentage of elongation at this time is called "ductility".
Both the strength and the ductility are essential basic quality of sewing thread. For example, as to the
strength, when sewing heavy-weight materials, it is necessary to sew with sewing thread having high
strength since thread breakage is apt to occur. It is the same in case of preventing thread breakage or
puncture when wearing the clothes. As to the ductility, if it is excessive, it will be the cause of seam
puckering or stitch skipping, and if it is too low, it may be the cause of thread breakage.
In addition, when wearing clothes, thread breakage may occur unless there is the proper ductility.Both
strength and ductility depend on material, processing method and count of sewing thread. Accordingly, it is
necessary to select a proper sewing thread after considering sewing conditions, application of sewing
products, etc. Normally, when the strength and the ductility are simply used, they mean "pull strength and
pull ductility". For other items, there are "hook strength and hook ductility" and "knotting strength and
knotting ductility".
Strength and ductility of the sewing thread (Strength conforms to JIS and ductility is shown low.)
<Table 㸌-4>
Kind No. Strength Polyester sewing thread Nylon sewing thread Cotton
Ductility Filament Spinning Filament Wooly sewing thread
50 gf 1010 1110 950 710
% 22 18 30 8
110d (1x2) gf 850
High % 35
ductility
* The above figures slightly differ among the respective thread manufacturers. Use them as reference values
