THREADS AND FASTENERS - Goodheart-Willcox

Thread Representation
A true projection view of a screw thread is
not used due to the helical shape. Instead,
threads are represented on a print in conventional
ways. The three conventional methods in
which threads may be represented on drawings
are the detailed, schematic, and simplified methods.
See Figure 11-3.
The detailed convention most closely represents
screw threads as they actually appear. This
convention is sometimes used to show the
geometry of a thread form as a portion of a
greatly enlarged detail on a drawing. A rule of
thumb is to draw detailed threads if the major
diameter appears larger than 1″ on the drawing.
The schematic convention and simplified
convention are representations of the thread and
are easier to draw. These conventions are recommended
when the major diameter is less than 1″
on the drawing. Both conventions are commonly
used to save drafting time. The simplified
convention is the easiest convention to use with
most CAD systems.
EXTERNAL THREADS
REGULAR VIEWS SECTION VIEWS
DETAILED REPRESENTATION
SCHEMATIC REPRESENTATION
SIMPLIFIED REPRESENTATION
Unit 11 Threads and Fasteners 133
Thread Series
There are four series of Unified screw
threads—coarse, fine, extra fine, and constantpitch.
See Figure 11-4 and Figure 11-5. Each
series has its own designation. There are also
three special thread series designated UNS, NS,
and UN. These series cover special combinations
of diameter, pitch, and length of engagement.
The Unified coarse thread series is designated
UNC. It is used for nuts, bolts, screws, and
general uses where a fine thread is not required.
The Unified fine thread series is designated
UNF. It is used where the length of the threaded
engagement is short and where a small lead
angle is desired.
The Unified extra fine series is designated
UNEF. It is used for very short lengths of thread
engagement and for thin-wall tubes, nuts, ferrules,
and couplings.
The Unified constant-pitch series is designated
UN with the number of threads per inch
INTERNAL THREADS
Figure 11-3.
The three conventional methods for representing threads are detailed, schematic, and simplified.
134 Print Reading for Industry
NORMAL
DIAMETER
BASIC
DIAMETER
COARSE
NC & UNC
THDS
PER
IN
TAP
DRILL
DIA
FINE
NF & UNF
THDS
PER
IN
TAP
DRILL
DIA
EXTRA FINE
NEF & UNEF
THDS TAP
PER DRILL
IN DIA NORMAL
0 .060 80 .0469
1 .073 64 No.53 72 No.53
2 .086 56 No.50 64 No.50
3 .099 48 No.47 56 No.45
4 .112 40 No.43 48 No.42
5 .125 40 No.38 44 No.37
6 .138 32 No.36 40 No.33
8 .164 32 No.29 36 No.29
10 .190 24 No.25 32 No.21
12 .216 24 No.16 28 No.14 32 No.13
1/4 .250 20 No.7 28 No.3 32 .2189
5/16 .3125 18 F 24 I 32 .2813
3/8 .375 16 .3125 24 Q 32 .3438
7/16 .4375 14 U 20 .3906 28 .4062
1/2 .500 13 .4219 20 .4531 28 .4688
9/16 .5625 12 .4844 18 .5156 24 .5156
5/8 .625 11 .5313 18 .5781 24 .5781
11/16 .6875 ... ... ... ... 24 .6406
3/4 .750 10 .6563 16 .6875 20 .7031
13/16 .8125 ... ... ... ... 20 .7656
7/8 .875 9 .7656 14 .8125 20 .8281
15/16 .9375 ... ... ... ... 20 .8906
Figure 11-4.
Thread specifications for NC, UNC, NF, UNF, NEF, and UNEF threads.
NORMAL
DIAMETER
8 PITCH
8N & 8UN
THDS
PER
IN
TAP
DRILL
DIA
12 PITCH
12N & 12UNF
THDS
PER
IN
TAP
DRILL
DIA
16 PITCH
16N & 16UN
THDS
PER
IN
TAP
DRILL
.500 ... ... 12 .422 ... ...
.563 ... ... 12 .484 ... ...
.625 ... ... 12 .547 ... ...
.688 ... ... 12 .609 ... ...
.750 ... ... 12 .672 16 .688
.813 ... ... 12 .734 16 .750
.875 ... ... 12 .797 16 .813
.934 ... ... 12 .869 16 .875
1.000 8 .875 12 .922 16 .938
1.063 ... ... 12 .984 16 1.000
1.125 8 1.000 12 1.047 16 1.065
1.188 ... ... 12 1.109 16 1.125
1.250 8 1.125 12 1.72 16 1.188
1.313 ... ... 12 1.234 16 1.250
1.375 8 1.250 12 1.297 16 1.313
1.434 ... ... 12 1.359 16 1.375
1.500 8 1.375 12 1.422 16 1.438
1.563 ... ... ... ... 16 1.500
1.625 8 1.500 12 1.547 16 1.563
1.688 ... ... ... ... 16 1.625
1.750 8 1.625 12 1.672 16 1.688
1.813 ... ... ... ... 16 1.750
1.875 8 1.750 12 1.797 16 1.813
1.934 ... ... ... ... 16 1.875
2.000 8 1.875 12 1.922 16 1.938
Figure 11-5.
Thread specifications for constant pitch threads.
DIA NORMAL
DIAMETER
BASIC
DIAMETER
COARSE
NC & UNC
THDS
PER
IN
TAP
DRILL
DIA
FINE
NF & UNF
THDS
PER
IN
TAP
DRILL
DIA
EXTRA FINE
NEF & UNEF
THDS
PER
IN
TAP
DRILL
DIA
1 1.000 8 .875 12 .922 20 .953
1–1/16 1.063 ... ... ... ... 18 1.000
1–1/8 1.125 7 .904 12 1.046 18 1.070
1–3/16 1.188 ... ... ... ... 18 1.141
1–1/4 1.250 7 1.109 12 1.172 18 1.188
1–5/16 1.313 ... ... ... ... 18 1.266
1–3/8 1.375 6 1.219 12 1.297 18 1.313
1–7/16 1.438 ... ... ... ... 18 1.375
1–1/2 1.500 6 1.344 12 1.422 18 1.438
1–9/16 1.563 ... ... ... ... 18 1.500
1–5/8 1.625 ... ... ... ... 18 1.563
1–11/16 1.688 ... ... ... ... 18 1.625
1–3/4 1.750 5 1.563 ... ... ... ...
2 2.000 4.5 1.781 ... ... ... ...
2–1/4 2.250 4.5 2.031 ... ... ... ...
2–1/2 2.500 4 2.250 ... ... ... ...
2–3/4 2.750 4 2.500 ... ... ... ...
3 3.000 4 2.750 ... ... ... ...
3–1/4 3.250 4 ... ... ... ... ...
3–1/2 3.500 4 ... ... ... ... ...
3–3/4 3.750 4 ... ... ... ... ...
4 4.000 4 ... ... ... ... ...
DIAMETER
8 PITCH
8N & 8UN
THDS
PER
IN
TAP
DRILL
DIA
12 PITCH
12N & 12UNF
THDS
PER
IN
TAP
DRILL
DIA
16 PITCH
16N & 16UN
THDS
PER
IN
TAP
DRILL
DIA
2.063 ... ... ... ... 16 2.000
2.125 ... ... 12 2.047 16 2.063
2.188 ... ... ... ... 16 2.125
2.250 8 2.125 12 2.172 16 2.188
2.313 ... ... ... ... 16 2.250
2.375 ... ... 12 2.297 16 2.313
2.438 ... ... ... ... 16 2.375
2.500 8 2.375 12 2.422 16 2.438
2.625 ... ... 12 2.547 16 2.563
2.750 8 2.625 12 2.717 16 2.688
2.875 ... ... 12 ... 16 ...
3.000 8 2.875 12 ... 16 ...
3.125 ... ... 12 ... 16 ...
3.250 8 ... 12 ... 16 ...
3.375 ... ... 12 ... 16 ...
3.500 8 ... 12 ... 16 ...
3.625 ... ... 12 ... 16 ...
3.750 8 ... ... ... 16 ...
3.875 ... ... 12 ... 16 ...
4.000 8 ... ... ... 16 ...
4.250 8 ... 12 ... 16 ...
4.500 8 ... ... ... 16 ...
4.750 8 ... 12 ... 16 ...
5.000 8 ... ... ... 16 ...
5.250 8 ... 12 ... 16 ...