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Steps FOR READING DIMENSIONS
1. 1
Many different sizes.
Read the numbers. They will look something like one of these:
o #4-40 x .5
o 1/4-20 x 5/8
o M3-50 x 10
2. 2
The major diameter for the threaded portion of the screw.
Interpret the first number. The first number gives the major, or largest, diameter.
o In Unified threads (measured in inches) there are numbered diameters #0 through #10, with 0
the smallest and 10 the largest. (Diameters #12 and #14 may also be found, but are usually on older
equipment and needed for repairs or restorations. #14 is close to, but not exactly the same as, 1/4-
inch.) The major diameter in Unified threads = 0.060" + 0.013"*(numbered diameter). So #2 has a
major diameter of 0.086". The odd numbers exist, but the even numbers are in far more common use.
o For screws larger than a #10, the diameters are listed in fractional inches. For instance, a 1/4-
20 screw has a 1/4-inch major diameter.
http://www.wikihow.com/Image:Screwthreaddia.jpghttp://www.wikihow.com/Image:Screwthreaddia.jpghttp://www.wikihow.com/Image:Screwthreadcallout1.jpghttp://www.wikihow.com/Image:Screwthreadcallout1.jpg8/3/2019 Steps for Reading Dimensions
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o For metric threads, e.g. M3.5, the number following the M is the major diameter of the external
thread in millimeters.
3. 3
The distance between adjacent threads, or thread pitch.
Interpret the second number. It has to do with the distance between adjacent threads. It may be given as the
number of threads per unit length; or it may be given as the distance between threads, also called the thread
pitch.
o For Unified threads, the number given is threads per inch. For instance, a 1/4-20 screw has
20 threads per inch.
o For metric threads, the thread pitch is given in millimeters per thread. Thus, an M2 x 0.4 screw
has threads every 0.4mm. Although most metric fasteners have two or more standard pitches (fine &
coarse threads), the pitch is often omitted from a thread callout, it is always helpful to carry a sample
with you to the hardware store.
There are two major metric "industrial standards": DIN Deutsches Institut fr
Normung (German) and the JIS Japanese Industrial Standards. Although these standards are
closely related and often identical, there will be cases where say a JIS M8 bolt may not have
the same pitch as a DIN M8 bolt.
4. 4
The length of most screws is measured from the bottom of the head.
http://www.wikihow.com/Image:Screwthreadlength.jpghttp://www.wikihow.com/Image:Screwthreadlength.jpghttp://www.wikihow.com/Image:Screwthreadpitch.jpghttp://www.wikihow.com/Image:Screwthreadpitch.jpg8/3/2019 Steps for Reading Dimensions
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Read the length, which is generally given after the "x". The length of most screws is measured from the
bottom of the head, as shown. Note, however, that a flathead screw, designed to sit flush in a countersunk
material, is measured to the top of the head.
o For unified threads the length is given in inches. A 1/4-20 x 3/4 screw is .75 inches long. The
length may be given in fractional inches or the decimal equivalent.
o For metric threads, the length is given in millimeters.
5. 5
Understand some other nomenclature that sometimes goes with screw threads.
o
Nuts have internal threads.
Thread classes refer to fit, how loosely or tightly the screw fits in the nut. The most common thread
classes are 2A or 2B. A indicates an external thread, such as on a screw or bolt. B indicates aninternal thread, such as on a nut. The 2 (or, far less commonly, 1 or 3) describes the tightness of the
fit.
o You may see the abbreviations UNC and UNF. These stand for unified coarse and unified
fine, respectively, and they refer to standard series of thread pitch. Each series assigns a pitch to
diameter. For instance, a #10 UNC screw has 24 threads per inch, whereas a #10 UNF screw has 32
threads per inch. If a thread is specified by its series, look for the pitch in a table.
o Minor diameter is the smallest diameter of the thread, the innermost diameter. Major diameter
is the largest diameter of the thread, the outermost diameter. The diameter given is typically the
nominal major diameter of an external, or male, thread.
6. 6
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American/United National Threads
Size DiameterTPI
Coarse
TPI
Fine
Root Dia.
Coarse
Hex
Head
Size
SAE
Washer
ID
SAE
Washer
OD
SAE
Washer
Thickness
#0 0.0600 - 80 0.0447
#1 0.0730 64 72 0.0560
#2 0.0860 56 64 0.0668 3/32"1/4"
1/32"
#3 0.0990 48 56 0.0771
#4 0.1120 40 48 0.0813 1/8"5/16"
1/32"
#5 0.1250 40 44 0.0971
#6 0.1380 32 40 0.1073 5/32"3/8"
3/64"
#8 0.1640 32 36 0.1299 3/16"7/16"
3/64"
#10 0.1900 24 32 0.1570 7/32"1/2"
1/16"
#12 0.2160 24 28 0.1722 1/4"9/16"
1/16"1/4" 0.2500 20 28 0.1850
3/8"9/32"
5/8"1/16"
5/16" 0.3125 18 24 0.24001/2"
11/32"11/16"
1/16"
3/8" 0.3750 16 24 0.2940 9/16" 13/32" 13/16" 1/16"7/16" 0.4375 14 20 0.3440
5/8"15/32"
15/16"1/16"
1/2" 0.5000 13 20 0.40003/4"
17/32" 1-1/16"
3/32"9/16" 0.5625 12 18 0.4540
7/8"19/32" 1-
3/16"3/32"
5/8" 0.6250 11 18 0.507015/16"
21/32" 1-5/16"
3/32"3/4" 0.7500 10 16 0.6200 1-
1/8"13/16" 1-
1/2"1/8"
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7/8" 0.8750 9 14 0.7310 1-5/16"
15/16" 1-3/4"
1/8"
1" 1.0000 8 12 0.8370 1-1/2" 1-1/16" 1-
3/4"1/8"
Metric Threads
Metric threads use the same thread profile as SAE threads. The biggest difference is that the
thread pitch (distance between consecutive threads) is given instead of threads per unit distance.
Diameter
Coarse
Pitch
mm
Fine
Pitch
mm
Root Dia.
Coarse
mm
Hex
Head
Size
mm
ISO
Washer
ID
mm
ISO
Washer
OD
mm
ISO
Washer
Thickness
mm
1 0.25 0.7294
1.1 0.25 0.8294
1.2 0.25 0.9294
1.4 0.30 1.075
1.6 0.35 1.221 3.2
1.8 0.35 1.421
2 0.40 1.567 4
2.2 0.45 1.713
2.5 0.45 2.013 5
3 0.50 2.459 5.5 3.4 7.0 0.6
3.5 0.60 2.850
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4 0.70 0.50 3.242 7 4.5 9.0 0.9
4.5 0.75 0.50 3.688
5 0.80 0.50 4.134 8 5.5 10 11
5.5 0.50
6 1.00 0.50 4.917 10 6.7 12.5 1.8
7 1.00 0.75 5.917
8 1.25 0.75 6.647 13 8.7 17 1.8
9 1.25 0.75 7.647
10 1.50 0.75 8.376 16 10.9 21 2.2
11 1.50 0.75 9.376
12 1.75 0.75 10.11 18 13.4 24 2.7
14 2.00 1.00 11.83 21
16 2.00 1.00 13.83 24 17.4 30 3.318 2.50 1.00 15.29
20 2.50 1.00 17.29 30 21.5 37.9 3.3
Bolt Strength
Bolt Strength
The Society of Automotive Engineering has issued standard J429, which sets forth standards forboth strength. The SAE grade of a bolt is marked on it's head in the form of short radial lines, the
number of lines being two less than the SAE grade (i.e.. 3 lines for grade 5).
SAE Grade Size Range Strength (psi)
1 1/4" to 1-1/2" 60,000
2 1/4" to3/4" 74,000
2 7/8" to 1-1/2" 60,000
5 1/4" to 1" 120,000
5 1-1/8" to 1-1/2" 105,000
7 1/4" to 1-1/2" 133,000
8 1/4" to 1-1/2" 150,000
ASTM standards are sometimes used as well; A325 bolts are the equivalent of SAE 5, and A490
bolts are the equivalent of SAE 8.
Preload
A very misunderstood part of bolting stuff together ispreload, which is the tension placed on the
bolt by the nut (as opposed to the load). A sufficiently high preload will protect the bolt from
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fatigue as the load changes, as the varying load will change the clamping force on the bolted
components, rather than the tension on the bolt. (This is not strictly true, but for a tinkerer like
me, it's adequate.) As a rule of thumb, the preload should exceed the maximum load by 15% orso.
In order for this to work, however, the joint must be stiffer than the bolt. For this reason, theshank of high-tech bolts are often necked down to the same diameter of the root of the thread. As
long as it isn't thinner than the root of the thread, it isn't any weaker than the thread, and thereforedoesn't effect overall bolt strength, but it is significantly less stiff than the original shank.
There are two ways to measure preload on a bolt; a torque wrench, and by measuring the angle
the nut has turned. Of the two, the latter is more accurate, as friction plays a significant - and
more importantly, indeterminate - role when using a torque wrench.
Torque = K preload diameter
K, the so-calledNut Factor, usually varies between 0.3 and 0.1, and is very sensitive to a numberof factors, ranging from temperature to thread condition, even to how fast the bolt is tightened.
Measuring the angle the nut has turned is simply measuring how much the bolt is stretching,
equal to the pitch (distance between threads) times the number of turns. Using this requires thatthe components being bolted don't compress much (or compress a known amount), and that the
"spring rate" of the bolt be known.
Turns = preload (spring rate pitch)
For example, if the "spring rate" of a 1/2-13 bolt is 50,000 pounds per inch (note that I made that
up, and that most bolts will yield longbefore stretching an inch), and you need 500 pounds ofpreload, you'll need to stretch the bolt 500 50000 = 0.01 inch. At 13 threads per inch (0.0769
inches per thread), this would equate to 0.13 turns, or about 45 past snug.
If more than one bolt is used in a joint, and those bolts are closer together than about fourdiameters, the preload on one bolt will effect the preload on the other bolts by compressing the
joint. This effect is called "crosstalk", and then all bets are off. Joints that are significantly less
stiff than the bolts, such as joints involving gaskets, suffer much worse from crosstalk. The bestway to control crosstalk is to use a carefully thought out tightening sequence (usually a spiral
starting at the center, or for circular patterns, alternating bolts), and to tighten the bolts in small
steps. Even so, it's a crap shoot.
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Table of Bolt Sizes ...ISO metric precision hexagon bolts , Coarse Thread Series,Bolt tolerance class 6g
Thread Form to BS 3643
Nominal (D) Thread. Bolt dia Bolt Head Bolt Nut
Size PitchMajor(d)
max - minMinor(d3 )max - min
PitchDiameter (d2
)max - min
Thick (Zb)Acc/Flats
(A/F)max - min
Acc./Corn(A/C)
M3 0,5 2,980 - 2,874 2,439 -2,272 2,655 - 2,580 2,125 5,50 - 5,38 6,40
M4 0,7 3,978 - 3,838 3,220 - 3,002 3,523 - 3,433 2,925 7,00 - 6,85 8,10
M5 0,8 4,976 - 4,826 3,869 - 4,110 4,456 - 4,361 3,650 8,00 - 7,85 9,20
M6 1,0 5,974 - 5,794 4,891 - 4,596 5,324 - 5,212 4,150 10,00 - 9,78 11,50
M8 1,25 7,972 - 7,760 6,272 - 6,619 7,160 - 7,042 5,650 13,00 - 12,73 15,00
M10 1,5 9,968 - 9,732 8,344 - 7,938 8,994 - 8,862 7,180 17,00 - 16,73 19,60
M12 1,7511,966 -11,701
10,072 -9,601
10,829 -10,679
8,180 19,00 - 18,67 22,10
M16 2,0 15,962 -15,682 13,797 -13,271 14,663 -14,503 10,180 24,00 - 23,67 27,70
M20 2,519,958 -19,623
17,252 -16,624
18,334 -18,164
13,215 30,00 - 29,67 34,60
M24 3,023,952 -23,577
20,701 -19,955
22,003 -21,803
15,215 36,00 - 35,58 41,60
M30 3,5029,947 -29,522
26,158 -25,306
27,674 -27,462
19,260 46,00 - 45,38 53,1
M36 4,0035,940 -35,465
31,610 -30,654
33,342 -33,118
23,260 55,00 - 54,26 63,5
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Nuts Sizes, Coarse Thread Series
Nut tolerance class 6H are dimensioned in BS3692
Thread form to BS 3643
Nominal Thread. Nut Diameter Nut
Size Pitch Major (D)Minor (D1 )Max - min
Thick (Zn)
M3 0,5 3,000 2,599 - 2,459 2,40
M4 0,7 4,000 3,422 - 3,242 3,20
M5 0,8 5,000 4,334 - 4,134 4,00
M6 1,0 6,000 5,153 - 4,917 5,00
M8 1,25 8,000 6,912 - 6,647 6,50
M10 1,5 10,000 8,676 - 8,376 8,00
M12 1,75 12,00010,441 -10,106
10,00
M16 2,0 16,00014,210 -13,835
13,00
M20 2,5 20,00017,744 -17,294
16,00
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M24 3,0 24,00021,252 -20,752
19,00
M30 3,5 30,00026,771 -26,211
24,00
M36 4,0 36,0032,270 -31,670
29,00
Bolt Sizes ...ISO metric precision hexagon bolts , Fine thread series
Bolt tolerance class 6g are dimensioned in BS3692:1967
Nominal Thread. Bolt dia (d) Bolt Head Bolt Nut
Size PitchMajor
max - minMinor
max - min
PitchDiametermax - min
Thick (Zb)Acc/Flatsmax - min
(A/F)
Acc./Corn(A/C)
M6 0,75 5,978 - 5,838 5,166 - 4,929 5,491 - 5,391 4,150 10,00 - 9,78 11,50
M8 1,00 7,974 - 7,794 6,891 - 6,596 7,324 - 7,212 5,650 13,00 - 12,73 15,00
M10 1,25 9,972 - 9,760 8,619 - 8,272 9,160 - 9,042 7,180 17,00 - 16,73 19,60
M12 1,2511,972 -11,760
10,619 -10,258
11,160 -11,028
8,180 19,00 - 18,67 22,10
M16 1,5015,968 -15,732
14,344 -13,930
14,994 -14,854
10,180 24,00 - 23,67 27,70
M20 1,519,968 -19,732
18,344 -17,930
18,994 -18,854
13,215 30,00 - 29,67 34,60
M24 2,023,962 -23,682
21,797 -21,261
22,663 -22,493
15,215 36,00 - 35,58 41,60
M30 2,029,962 -29,682
27,797 -27,261
28,663 -28,493
19,260 46,00 - 45,38 53,1
M36 3,0035,952 -35,577
32,704 -31,955
34,003 -33,803
23,260 55,00 - 54,26 63,5
Nuts Sizes - Fine Thread Series..
Nut tolerance class 6H are dimensioned in BS3692:1967
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Nominal Thread. Nut Diameter Nut
Size Pitch MajorMinor
Max - minThick (Zn)
M6 0,75 6,000 5,378 - 5,188 5,00
M8 1,00 8,000 7,153 - 6,917 6,50
M10 1,25 10,000 8,912 - 8,647 8,00
M12 1,25 12,000
10,912 -
10,647 10,00
M16 1,50 16,00014,676 -14,376
13,00
M20 1,50 20,00018,676 -18,376
16,00
M24 2,0 24,00022,210 -21,835
19,00
M30 2,0 30,00028,210 -27,835
24,00
M36 3,0 36,0033,252 -32,752
29,00
Washers.. Plain Washers , bright metric series
Bright Washers are dimensioned in BS4320: 1968
Nominal Washer Diameter Washer Thickness
SizeInternal
max - minExternal
max - minThick
max - minThin
M3 3,4 - 3,2 7,0 - 6,7 0,6 - 0,4 -
M4 4,5 - 4,3 9,0 - 8,7 0,9 - 0,7 -
M5 5,5 - 5,3 10,0 - 9,7 1,1 - 0,9 -
M6 6,7 - 6,4 12,5 - 12,1 1,8 - 1,4 0,9 - 0,7
M8 8,7 - 8,4 17,0 - 16,6 1,8 - 1,4 1,1 - 0,9
M10 10,9 - 10,5 21,0 - 20,5 2,2 - 1,8 1,45 - 1,05
M12 13,4 - 13,0 24,0 - 23,5 2,7 - 2,3 1,8 - 1,4
M16 17,4 - 17,00 30,0 - 29,5 3,3 - 2,7 2,2 - 1,8
M20 21,5 - 21,0 37,0 - 36,2 3,3 - 2,7 2,2 - 1,8
M24 25,5 - 25,0 44,0 - 43,2 4,3 - 3,7 2,7 - 2,3
M30 31,6 - 31,0 56,0 - 55,0 4,3 - 3,7 2,7 - 2,3
M36 37,6 - 37,0 66,0 - 65,0 5,6 - 4,4 3,3 - 2,7
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Washers.. Plain Washers , Black metric series
Black Washers are dimensioned in BS4320: 1968
Nominal Washer DiameterWasher
Thickness
SizeInternal
max - minExternal
max - minThicknessmax - min
M5 5,8 - 5,5 10,0 - 9,2 1,2 - 0,8
M6 7,0 - 6,6 12,5 - 11,7 1,9 - 1,3
M8 9,4 - 9,0 17,0 - 16,2 1,9 - 1,3
M10 11,5 - 11,0 21,0 - 20,2 2,3 - 1,7
M12 14,5 - 14,0 24,0 - 23,2 2,8 - 2,2
M16 18,5 - 18,00 30,0 - 29,2 3,6 - 2,4
M20 22,6 - 22,0 37,0 - 35,8 3,6 - 2,4
M24 26,6 - 26,0 44,0 - 42,8 4,6 - 3,4
M30 33,8 - 33,0 56,0 - 54,5 4,6 - 3,4
M36 39,8 - 39,0 66,0 - 64,5 6,0 - 4,0
M42 45,8 - 45,0 78,0 - 76,5 8,2 - 5,8
M48 53,0 - 52,0 92,0 -90,0 9,2 - 6,8
Grade and Strength Information
There are numerous standards that fasteners are manufactured to, and those standards describe
everything from material chemistry to surface finish to heat treatment. The most relevant numbers are
"Proof Stress," "Yield Stress" and "Tensile / Ultimate Stress." Tensile Strength is how much stress the
material can withstand before finally ripping apart. Yield Stress is the amount of stress that a material can
undergo before permanently stretching. Proof stress is similar to Yield stress except that it is slightly less
(about 90%), and only applies to fasteners. The thread geometry causes them to yield slightly before the
Yield stress level of the material, so Proof Stress can be thought of the true yield--in other words, the
fastener will behave like a spring below that stress level.
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So which of these numbers should be used? While there are many arguments for tightening a screw
past its yield point (for instance), from this author's viewpoint, if an external load yields a screw, and if that
load is ever removed, the screw will now be permanently stretched and loose. Therefore, we recommend
designing so that the combined internal and external loads stay below the proof stress to avoid
any possibility of yielding. If proof stress is unknown, 85% of Yield stress can be used as an
approximation. The ultimate or tensile stress is sometimes designed to, but we do not know when this
acceptable or not. Also, the ultimate stress is used in designing joints for alternating loads, but this isbeyond our scope.
Several organizations publish standards for fasteners. For inch/english, this includes SAE, ASTM, ANSI,
ASME and others, although the most commonly used are the SAE "Grades." (standard J429). The most
common metric specifications are published by the ISO. (ANSI metric specs agree with ISO for all
practical purposes--Machinery's Handbook)
Common Inch / Imperial SAE Grades: (all values in ksi or 1000 lbs /
square inch)
HeadMarking
Grade Diameter (in) Proof Strength Yield Strength Tensile (Ultimate)
Strength
2 1/4 to 3/4 55 57 74
3/4 to 1-1/2 33 36 60
5 1/4 to 1 85 92 120
1 to 1-1/2 74 81 105
8 1/4 to 1-1/2 120 130 150
Socket Head Cap Screws made from alloy steel are typically manufactured to a higher strength than SAE
Grade 8: 180 ksi tensile strength for fasteners up to 1/2 inch, 170 ksi for larger sizes (ASTM A574, p. G-
34).
For many more head markings and their corresponding specifications, see here.
Metric ISO Marking
Metric fasteners are marked with two numbers separated by a decimal point, like 10.9. The 10 is 1/100 of
tensile strength in MPa, and the .9 represents the ratio of yield to tensile strength. So 10.9 represents a
tensile strength of 1000 MPa and yield of 900 MPa. Some strengths are stronger than this method shows,
see table 10 on this page. Other references for this table: hereandhere.
Grade size range proof
strength (MPa)
approx yield
strength (MPa)
tensile
strength (MPa)
approx equiv.
to SAE grade:
http://www.appliedbolting.com/pdf/yielding.pdfhttp://www.appliedbolting.com/pdf/yielding.pdfhttp://www.americanfastener.com/technical/grade_markings_steel.asphttp://www.americanfastener.com/technical/grade_markings_steel.asphttp://euler9.tripod.com/bolt-database/22.htmlhttp://www.utm.edu/departments/engin/lemaster/Machine%20Design/Lecture%2028.pdfhttp://www.utm.edu/departments/engin/lemaster/Machine%20Design/Lecture%2028.pdfhttp://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspxhttp://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspxhttp://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspxhttp://www.appliedbolting.com/pdf/yielding.pdfhttp://www.americanfastener.com/technical/grade_markings_steel.asphttp://euler9.tripod.com/bolt-database/22.htmlhttp://www.utm.edu/departments/engin/lemaster/Machine%20Design/Lecture%2028.pdfhttp://www.boltdepot.com/fastener-information/Materials-and-Grades/Bolt-Grade-Chart.aspx8/3/2019 Steps for Reading Dimensions
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grade dec x tensile*
4.8 M1.6-M16 310 336 420 SAE 2
8.8 < M16 580 640 800 SAE 5
M16-M76 600 660 830
10.9 > M5 830 940 1040 SAE 8
12.9 M1.6-M100 970 1100 1220 ASTM-A574
alloy socket
screws
*these value aren't necessarily from the standards, they're calculated as described above.
Tensile stress areas and acceptable load estimates for various grades
For applications where there is any chance of bodily or property harm, don't rely on our external load
estimates--they are intended to give a rough approximation of what screws of various grades can
hold in non-critical applications, and are based on the following assumptions:
We use the proof strength as the maximum stress that should be endured from the combined
internal (original tightening) and external loads.
If proof load isn't specified in the above tables, we use 85% of yield
It is assumed that the joint is twice as stiff as the bolt, which implies that 1/3 of the external load is
seen by the bolt, and the other 2/3 goes into reducing clamping load. The forumla explained above
and used below is 60% * proof * tensile area / 1.0 (safety factor). We recommend using a 2.5safety factor for non-critical / costly applications--ie, divide the numbers below by 2.5.For joints
clamping aluminum, plastic, gaskets or other softer material it's safer to assume that 100% of external
load is seen by the fastener (multiply by 20% instead of 60%).
tensile stress area:Tests have shown that the average of the minor and pitch diameters
approximates the effective area of a fastener. The Machinery's handbook has a different formula for
bolts with tensile strengths over 100ksi, but due to some doubtabout its origins, we don't use it.
As far as we can tell, SAE Grades apply only to bolts at least 1/4" in diameter. Any unmarked
machine screws smaller than that are probably Grade 2; we show the higher Grades for reference
only on those sizes. Alloy steel socket head cap screws will most likely have a greater strength than
SAE Grade 8 unless their manufacturer says otherwise.
We assume shear loads and torsional loads from tightening are zero.
For alloy socket screws, yield strength is 180 ksi until 1/2" and 170 ksi for larger diameters. Weuse 85% of these values to approximate proof strength.
Inch tensile areas and loads (in lbs), both fine and coarse thread
size - dec. major tensile Grade 2 Grade 5 Grade 8 alloy socket
http://www.eng-tips.com/viewthread.cfm?qid=33175&page=2http://www.eng-tips.com/viewthread.cfm?qid=33175&page=2http://www.eng-tips.com/viewthread.cfm?qid=33175&page=28/3/2019 Steps for Reading Dimensions
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threads / in diameter (in) stress area
square inches
(proof strength:
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3/4-10 .75 .334 6613.2 17034 24048 28957.8
3/4-16 .75 .373 7385.4 19023 26856 32339.1
7/8-9 .875 .462 9147.6 23562 33264 40055.4
7/8-14 .875 .509 10078.2 25959 36648 44130.3
1-8 1.0 .606 11998.8 30906 43632 52540.2
1-12 1.0 .663 13127.4 33813 47736 57482.1
alternative load carrying recommendations: here.
Standard Thread Pitches
Coarse Thread Series (UNC/UNRC) is the most common designation for general application bolts and nuts. Coarse
thread is beneficial, because they are less likely to cross thread, more tolerant in adverse conditions and facilitate
quick assembly.
Fine Thread Series (UNF/UNRF) is commonly used in precision applications. Because of the larger tensile stress
areas, they have high tension strength. However, a longer engagement is required for fine thread applications than
for coarse series threads to prevent stripping.
8 - Thread Series (8UN) is the specified thread forming method for several ASTM standards including A193 B7,
A193 B8/B8M, and A320. This series is used for diameters one inch and above.
http://www.pencomsf.com/pdf/tech_info.pdfhttp://www.pencomsf.com/pdf/tech_info.pdf8/3/2019 Steps for Reading Dimensions
17/20
Coarse Thread Series -
UNCFine Thread Series - UNF 8-Thread Series - 8UN
Nomi
nal
Sizeand
Threa
ds
Per
In.
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Sizeand
Threa
ds Per
In.
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Sizeand
Threa
ds Per
In.
Basic
PitchDia.
Secti
on at
Minor
Dia.
Tensi
le
Stress
Area
In. Sq in. Sq in. In. Sq in. Sq in. In. Sq in. Sq in.
-- -- -- -- -- 0 - 800.051
9
0.0015
1
0.0018
0
-- -- -- -- --
1 - 640.062
9
0.0021
8
0.0026
31 - 72
0.064
0
0.0023
7
0.0027
8
2 - 560.074
4
0.0031
0
0.0037
02 - 64
0.075
9
0.0033
9
0.0039
4
3 - 480.085
5
0.0040
6
0.0048
73 - 56
0.087
4
0.0045
1
0.0052
3
4 - 400.095
8
0.0049
6
0.0060
44 - 48
0.098
5
0.0056
6
0.0066
1
-- -- -- -- --
5 - 40 0.1088
0.00672
0.00796
5 - 44 0.1102
0.00716
0.00830
6 - 320.117
7
0.0074
5
0.0090
96 - 40
0.121
8
0.0087
4
0.0101
5
8 - 320.143
7
0.0119
60.0140 8 - 36
0.146
0
0.0128
5
0.0147
4
10 -
24
0.162
9
0.0145
00.0175 10 - 32
0.169
70.0175 0.0200 -- -- -- -- --
12 -
24
0.188
90.02060.0242 12 - 28
0.192
80.0226 0.0258 -- -- -- -- --
14 - 200.217
50.0269 0.0318 14 - 28
0.226
80.0326 0.0364 -- -- -- -- --
516 - 0.276 0.04540.0524516 - 24 0.285 0.0524 0.0580 -- -- -- -- --
8/3/2019 Steps for Reading Dimensions
18/20
Coarse Thread Series -
UNCFine Thread Series - UNF 8-Thread Series - 8UN
Nomi
nal
Sizeand
Threa
ds
Per
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Size
and
Threa
ds Per
In.
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Size
and
Threa
ds Per
In.
Basic
PitchDia.
Secti
on at
Minor
Dia.
Tensi
le
Stress
Area
In. Sq in. Sq in. In. Sq in. Sq in. In. Sq in. Sq in.
18 4 4
38 - 160.334
40.0678 0.0775 38 - 24
0.347
90.0809 0.0878 -- -- -- -- --
7
16 -14 0.3911 0.0933 0.1063716 - 20 0.4050 0.1090 0.1187 -- -- -- -- --
12 - 130.450
00.1257 0.1419 12 - 20
0.467
50.1486 0.1599 -- -- -- -- --
916 -
12
0.508
40.162 0.182 916 - 18
0.526
40.189 0.203 -- -- -- -- --
58 - 110.566
00.202 0.226 58 - 18
0.588
90.240 0.256 -- -- -- -- --
34 - 100.685
00.302 0.334 34 - 16
0.709
40.351 0.373 -- -- -- -- --
78 - 90.802
80.419 0.462 78 - 14
0.828
60.480 0.509 -- -- -- -- --
1 - 80.918
80.551 0.606 1 - 12
0.945
90.625 0.663 1 - 8
0.918
80.551 0.606
118 - 71.032
20.693 0.763
118 -
12
1.070
90.812 0.856 118 - 8
1.043
80.728 0.790
114 - 71.157
20.890 0.969
114 -
12
1.195
91.024 1.073 114 - 8
1.168
80.929 1.000
138 - 61.266
71.054 1.155
138 -
12
1.320
91.260 1.315 138 - 8
1.293
81.155 1.233
112 - 6 1.391 1.294 1.405 112 - 1.445 1.521 1.581 1
12 - 8 1.418 1.405 1.492
8/3/2019 Steps for Reading Dimensions
19/20
Coarse Thread Series -
UNCFine Thread Series - UNF 8-Thread Series - 8UN
Nomi
nal
Sizeand
Threa
ds
Per
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Size
and
Threa
ds Per
In.
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Size
and
Threa
ds Per
In.
Basic
PitchDia.
Secti
on at
Minor
Dia.
Tensi
le
Stress
Area
In. Sq in. Sq in. In. Sq in. Sq in. In. Sq in. Sq in.
7 12 9 8
-- -- -- -- -- -- -- -- -- -- 158 - 81.543
81.68 1.78
134 - 5 1.6201 1.74 1.90 -- -- -- -- -- 134 - 8 1.6688 1.98 2.08
-- -- -- -- -- -- -- -- -- -- 178 - 81.793
82.30 2.41
2 - 4121.855
72.30 2.50 -- -- -- -- -- 2 - 8
1.918
82.65 2.77
214 -
4-12
2.105
73.02 3.25 -- -- -- -- -- 214 - 8
2.168
83.42 3.56
212 - 42.337
63.72 4.00 -- -- -- -- -- 212 - 8
2.418
84.29 4.44
234 - 42.587
64.62 4.93 -- -- -- -- -- 234 - 8
2.668
85.26 5.43
3 - 42.837
65.62 5.97 -- -- -- -- -- 3 - 8
2.918
86.32 6.51
314 - 43.087
66.72 7.10 -- -- -- -- -- 314 - 8
3.168
87.49 7.69
312 - 43.337
67.92 8.33 -- -- -- -- -- 312 - 8
3.418
88.75 8.96
334 - 43.587
69.21 9.66 -- -- -- -- -- 334 - 8
3.668
810.11 10.34
4 - 4 3.837 10.61 11.08 -- -- -- -- -- 4 - 8 3.918 11.57 11.81
8/3/2019 Steps for Reading Dimensions
20/20
Coarse Thread Series -
UNCFine Thread Series - UNF 8-Thread Series - 8UN
Nomi
nal
Sizeand
Threa
ds
Per
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Size
and
Threa
ds Per
In.
Basic
PitchDia.
Sectio
n at
Minor
Dia.
Tensil
e
Stress
Area
Nomin
al Size
and
Threa
ds Per
In.
Basic
PitchDia.
Secti
on at
Minor
Dia.
Tensi
le
Stress
Area
In. Sq in. Sq in. In. Sq in. Sq in. In. Sq in. Sq in.
6 8