Hex Nut Grade Identification and Mechanical Properties

How strong are these nuts?  That’s what she said.  Seriously, what do those marks mean?  Should I order a hex nut with one dot or three dashes?  Here’s a cheat sheet with nut identifying marks, material grade and mechanical properties.


Grade
Identification
Marking
Specification Material Nominal Size
In.
Proof
Load
Stress
ksi
Hardness
Rockwell
See
Note
Min Max

No Mark
ASTM A563 – Grade 0 Carbon Steel 1/4 thru 1-1/2 69 B55 C32 3,4
ASTM A563 – Grade A Carbon Steel 1/4 thru 1-1/2 90 B68 C32 3,4
ASTM A563 – Grade B Carbon Steel 1/4 thru 1 120 B69 C32 3,4
over 1 thru 1-1/2 105
ASTM A563 – Grade C Carbon Steel
May be Quenched
and Tampered
1/4 thru 4 144 B78 C38 5
ASTM A563 – Grade C3 Atmospheric
Corrosion
Resistant Steel
May be Quenched
and Tampered
1/4 thru 4 144 B78 C38 5,9
ASTM A563 – Grade D Carbon Steel
May be Quenched
and Tampered
1/4 thru 4 150 B84 C38 6
ASTM A563 – Grade DH Carbon Steel
Quenched
and Tampered
1/4 thru 4 175 C24 C38 6
ASTM A563 – Grade DH3 Atmospheric
Corrosion
Resistant Steel,
Quenched
and Tampered
1/4 thru 4 175 C24 C38 5,9
ASTM A194 – Grade 1 Carbon Steel 1/4 thru 4 130 B70 7
ASTM A194 – Grade 2 Medium Carbon
Steel
1/4 thru 4 150 159 352 7,8
ASTM A194 – Grade 2H Medium Carbon
Steel, Quenched
and Tempered
1/4 thru 4 175 C24 C38 7
ASTM A194 – Grade 2HM Medium Carbon
Steel, Quenched
and Tempered
1/4 thru 4 150 159 237 7,8
ASTM A194 – Grade 4 Medium Carbon
Alloy Steel,
Quenched
and Tempered
1/4 thru 4 175 C24 C38 7
ASTM A194 – Grade 7 Medium Carbon
Alloy Steel,
Quenched
and Tempered
1/4 thru 4 175 C24 C38 7
ASTM A194 – Grade 7M Medium Carbon
Alloy Steel,
Quenched
and Tempered
1/4 thru 4 150 159 237 7
See Note 1,2 10

Hex Bolt Identifying Marks, Material Grade and Mechanical Properties

Are you confused about the modest hex bolt, or are you wondering what all those marks mean?  This table will help you identify any hex bolt right on the nuts, and it will also tell you about the material grade and mechanical properties.  What more could you ask for from a super boring table?

Hex Bolt Identification
Grade Mark
Specification Fastener
Description
Material Nominal Size
Range (in.)
Mechanical Properties
Proof Load
(psi)
Yield Strength
Min (psi)
Tensile Strength
Min (psi)

No
Grade
Mark
SAE J429
Grade 1
Bolts,
Screws,
Studs
Low or Medium Carbon Steel 1/4 thru 1-1/2 33,000 36,000 60,000
ASTM A307
Grades A&B
Low Carbon Steel 1/4 thru 4
SAE J429
Grade 2
Low or Medium Carbon Steel 1/4 thru 3/4 Over 3/4 to 1-1/2 55,000
33,000
57,000
36,000
74,000
60,000

No
Grade
Mark
SAE J429
Grade 4
Studs Medium Carbon Cold Drawn Steel 1/4 thru 1-1/2 100,000 115,000

B5
ASTM A193
Grade B5
AISI 501 1/4 Thru 4 80,000 100,000

B6
ASTM A193
Grade B6
AISI 410 85,000 110,000

B7
ASTM A193
Grade B7
AISI 4140, 4142, OR 4105 1/4 thru 2-1/2
Over 2-1/2 thru 4
Over 4 thru 7


105,000
95,000
75,000
125,000
115,000
100,000

B16
ASTM A193
Grade B16
CrMoVa Alloy Steel 105,000
95,000
85,000
125,000
115,000
100,000

B8
ASTM A193
Grade B8
AISI 304 1/4 and larger 30,000 75,000

B8C
ASTM A193
Grade B8C
AISI 347

B8M
ASTM A193
Grade B8M
AISI 316

B8T
ASTM A193
Grade B8T
Bolts,
Screws,
Studs for High-Temperature Service
AISI 321 1/4 and larger 30,000 75,000

B8
ASTM A193
Grade B8
AISI 304
Strain Hardened
1/4 thr 3/4
Over 3/4 thru 1
Over 1 thru 1-1/4
Over 1-1/4 thru 1-1/2



100,000
80,000
65,000
50,000
125,000
115,000
105,000
100,000

B8C
ASTM A193
Grade B8C
AISI 347
Strain Hardened

B8M
ASTM A193
Grade B8M
AISI 316
Strain Hardened
95,000
80,000
65,000
50,000
110,000
100,000
95,000
90,000

B8T
ASTM A193
Grade B8T
AISI 321
Strain Hardened
100,000
80,000
65,000
50,000
125,000
115,000
105,000
100,000

L7
ASTM A320
Grade L7
Bolts,
Screws,
Studs for Low-Temperature Service
AISI 4140,
4142 or 4145
1/4 thru 2-1/2 105,000 125,000

L7A
ASTM A320
Grade L7A
AISI 4037

L7B
ASTM A320
Grade L7B
AISI 4137

L7C
ASTM A320
Grade LC7
AISI 8740

L43
ASTM A320
Grade L43
AISI 4340 1/4 thru 4 105,000 125,000

B8
ASTM A320
Grade B8
Bolts,
Screws,
Studs for Low-Temperature Service
AISI 304 1/4 and larger 30,000 75,000

B8C
ASTM A320
Grade B8C
AISI 347

B8T
ASTM A320
Grade B8T
AISI 321

B8F
ASTM A320
Grade B8F
AISI 303
or 303Se

B8M
ASTM A320
Grade B8M
AISI 316

B8
ASTM A320
Grade B8
AISI 304 1/4 thru 3/4
Over 3/4 thru 1
Over 1 thru 1-1/4
Over 1-1/4 thru 1-1/2



100,000
80,000
65,00
50,00
100,000
80,000
65,00
50,00

B8C
ASTM A320
Grade B8C
AISI 347

B8F
ASTM A320
Grade B8F
AISI 303
or 303Se

B8M
ASTM A320
Grade B8M
AISI 316

B8T
ASTM A320
Grade B8T
AISI 321
SAE J429
Grade 5
Bolts,
Screws,
Studs
Medium Carbon Steel, Quenched and Tempered 1/4 thru 1
Over 1 to 1-1/2
85,000
74,000
92,000
81,000
120,000
105,000
ASTM A449 1/4 thru 1
Over 1 to 1-1/2
Over 1-1/2 thru 3
85,000
74,000
55,000
92,000
81,000
58,000
120,000
105,000
90,000
SAE J429
Grade 5.1
Sems Low or Medium Carbon Steel, Quenched and Tempered No. 6
thru 3/8
85,000 120,000
SAE J429
Grade 5.2
Bolts,
Screws,
Studs
Low Carbon Martensitic Steel, Quenched and Tempered 1/4 thru 1 85,000 92,000 120,000

A325
ASTM A325
Type 1
High Strength
Structural Bolts
Medium Carbon Steel, Quenched and Tempered 1/2 thru 1
1-1/8 thru 1-1/2
85,000
74,000
92,000
81,000
120,000
105,000

A325
ASTM A325
Type 2
Low Carbon Martensitic Steel, Quenched and Tempered 1/2 thru 1 85,000 92,000 120,000

A325
ASTM A325
Type 3
Atmospheric Corrosion Resisting Steel, Quenched and Tempered 1/2 thru 1
1-1/8 thru 1-1/2
85,000
74,000
92,000
81,000
120,000
105,000

BB
ASTM A354
Grade BB
Bolts,
Studs
Alloy Steel, Quenched and Tempered 1/4 thru 2-1/2
2-3/4 thru 4
80,000
75,000
83,000
78,000
105,000
100,000

BC
ASTM A354
Grade BC
105,000
95,000
109,000
99,000
125,000
115,000
SAE J429
Grade 7
Bolts,
Screws,
Medium Carbon Alloy Steel, Quenched and Tempered 4 1/4 thru 1-1/2 105,000 115,000 133,000
SAE J429
Grade 8
Bolts,
Screws,
Studs
Medium Carbon Alloy Steel, Quenched and Tempered 1/4 thru 1-1/2 120,000 130,000 150,000
ASTM A354
Grade BD
Alloy Steel, Quenched and Tempered 4

No Grade
Mark
SAE J429
Grade 8.1
Studs Medium Carbon Alloy or SAE 1041 Modified Elevated Temperature Drawn Steel 1/4 thru 1-1/2 120,000 130,000 150,000

A490
ASTM A490 High Strength Structural Bolts Alloy Steel, Quenched and Tempered 1/2 thru 1-1/2 120,000 130,000 150,000 min
170,000 max

No Grade
Mark
ISO R898
Class 4.6
Bolts,
Screws,
Studs
Medium Carbon Steel, Quenched and Tempered All Sizes
thru 1-1/2
33,000 36,000 60,000

No Grade
Mark
ISO R898
Class 5.8
55,000 57,000 74,000
8.8

or

88
ISO R898
Class 8.8
Alloy Steel, Quenched and Tempered 85,000 92,000 120,000
10.9

or

109
ISO R898
Class 10.9
120,000 130,000 150,000

Your hex bolt may require a hex nut.

Flat Washer Dimensions (ASME B18.22.1)

How much space do you need for a bolt if you are using a flat washer?  How long do your threads need to be if you are accounting for the thickness of a washer.  Flat washer dimensions are frequently important while working on mechanical designs.  While there are many size options available, here is a table for the most common flat washer dimensions.


Bolt Size A B C Weight In Pounds
Per 100 Pieces
Inside Diameter Outside Diameter Thickness
3/8 7/16 1 0.083 2
1/2 9/16 1-3/8 0.109 4
5/8 11/16 1-3/4 0.134 8
3/4 13/16 2 0.148 11
7/8 15/16 2-1/4 0.165 15
1 1-1/16 2-1/2 0.165 19
1-1/8 1-1/4 2-3/4 0.165 22
1-1/4 1-3/8 3 0.165 26
1-3/8 1-1/2 3-1/4 0.180 33
1-1/2 1-5/8 3-1/2 0.180 38
1-5/8 1-3/4 3-3/4 0.180 43
1-3/4 1-7/8 4 0.180 50
1-7/8 2 4-1/4 0.180 57
2 2-1/8 4-1/2 0.180 63
2-1/4 2-3/8 4-3/4 0.220 83
2-1/2 2-5/8 5 0.238 96
2-3/4 2-7/8 5-1/4 0.259 110
3 3-1/8 5-1/2 0.284 130

Hex Nut Dimensions

There are lots of reasons you need to know hex nut dimensions.  You need to hex nut height to determine the best length of a fastener in a bolted assembly.  You need to know the size of the hex to make sure you have sufficient clearance for the nut itself, the washer and a wrench.


Size Across Flats* Height
Hex Nut Machine Screw Nut Hex Nut Jam Nut Nylock Nut Machine Screw Nut
0 5/32 3/64
1 5/32 3/64
2 3/16 9/64 1/16
3 3/16 9/64 1/16
4 1/4 9/64 3/32
6 5/16 11/64 7/64
8 11/32 15/64 1/8
10 3/8 15/64 1/8
12 7/16 5/16 5/32
1/4 7/16 7/16 7/32 5/32 5/16 3/16
5/16 1/2 9/16 17/64 3/16 11/32 7/32
3/8 9/16 5/8 21/64 7/32 29/64 1/4
7/16 11/16 3/8 1/4 29/64
1/2 3/4 7/16 5/16 19/32
9/16 7/8 31/64 5/16 41/64
5/8 15/16 35/64 3/8 3/4
3/4 1-1/8 41/64 27/64 7/8
7/8 1-5/16 3/4 31/64 63/64
1 1-1/2 55/64 35/64 1-3/64
* This is also the size of wrench to use.

Hex Cap Bolt Dimensions

Hex cap bolt dimensions are trickier than you think.  By default, they are not threaded all the way, so you need to be careful in your design to make sure you are not threading beyond the capability of the bolt itself.

Just as with the standard nut and washer, it it important to consider the geometric constraints of the hex cap bolt to ensure proper function and easier assembly / disassembly.


Hex Bolt Dimensions s
Basic Product Diameter
Full-Size Body Diameter
Width Across Flats
Width Across Corners
Head Height
Thread Length
Thread Length
Max
Min
Max
Min
Up to 6in
Over 6 in
1/4
.26
.237
7/16
.505
0.484
11/64
0.75
1.00
5/16
.324
.298
1/2
.577
0.552
7/32
0.88
1.13
3/8
.388
.360
9/16
.650
0.62
1/4
1.00
1.25
7/16
.452
.421
5/8
.722
0.687
19/64
1.13
1.38
1/2
.515
.482
3/4
.866
0.826
11/32
1.25
1.50
5/8
.642
.605
15/16
1.083
1.033
27/64
1.50
1.75
3/4
.768
.729
1-1/8
1.299
1.24
1/2
1.75
2.00
7/8
.895
.852
1-5/16
1.516
1.447
37/64
2.00
2.25
1
1.022
.976
1-1/2
1.732
1.653
43/64
2.25
2.50
1-1/8
1.149
1.098
1-11/16
1.949
1.859
3/4
2.50
2.75
1-1/4
1.277
1.223
1-7/8
2.165
2.066
27/32
2.75
3.00
1-3/8
1.404
1.345
2-1/16
2.382
2.273
29/32
3.00
3.25
1-1/2
1.531
1.47
2-1/4
2.598
2.48
1
3.25
3.50
1-3/4
1.785
1.716
2-5/8
3.031
2.893
1-5/32
3.75
4.00
2
2.039
1.964
3
3.464
3.306
1-11/32
4.25
4.50
2-1/4
2.305
2.214
3-3/8
3.897
3.719
1-1/2
4.75
5.00
2-1/2
2.559
2.461
3-3/4
4.33
4.133
1-21/32
5.25
5.5
2-3/4
2.827
2.711
4-1/8
4.763
4.546
1-13/16
5.75
6.00
3
3.081
2.961
4-1/2
5.196
4.959
2
6.25
6.50
3-1/4
3.335
3.21
4-7/8
5.629
5.372
2-3/16
6.75
7.00
3-1/2
3.589
3.461
5-1/4
6.062
5.786
2-5/16
7.25
7.50
3-3/4
3.858
3.726
5-5/8
6.495
6.198
2-1/2
7.75
8.00
4
4.111
3.975
6
6.928
6.612
2-11/16
8.25
8.50

 

Metric Thread – Tap Drill / Clearance Drill

Below is a table for metric tap drill sizes.  It covers both threaded holes (when you are cutting thread) and clearance holes (when you are simply placing a bolt through a hole).


Metric Tap Drill Chart
Tap size Major
Dia (mm)
Threads
per
Tap Drill
(mm)
Tap Drill
(inch)
Clearance Hole
(mm)
Clearance Hole
(inch)
M1.6×0.35 1.6 0.35 1.25 #55 1.8 #49
M2x0.4 2.0 0.40 1.60 #52 2.4 #41
M2.5×0.45 2.5 0.45 2.05 #46 2.9 #32
M3x.05 3.0 0.50 2.50 #39 3.4 #29
M3.5×0.6 3.5 0.60 2.90 #32 3.9 #23
M4x0.7 4.0 0.70 3.30 #30 4.5 #16
M5x0.8 5.0 0.80 4.20 #19 5.5 7/32
M6x1 6.0 1.00 5.0 #8 6.6 G
M8x1.25 8.0 1.25 6.8 H 9.0 T
M8x1 8.0 1.00 7.0 J 9.0 T
M10x1.5 10.0 1.50 8.5> R 12.0 31/64
M10x1.25 10.0 1.25 8.8 11/32 12.0 31/64
M12x1.75 12.0 1.75 10.2 13/32 14.0 35/64
M12x1.25 12.0 1.25 10.8 27/64 14.0 35/64
M14x2 14.0 2.00 12.0 15/32 16.0 5/8
M14x1.5 14.0 1.5 12.5 1/2 16.0 5/8
M16x2 16.0 2.00 14.0 35/64 18.0 45/64
M16x1.5 16.0 1.50 14.5 37/64 18.0 45/64
M18x2.5 18.0 2.50 15.5 39/64 20.0 51/64
M18x1.5 18.0 1.50 16.5 21/32 20.0 51/64
M20x2.5 20.0 2.50 17.5 11/16 22.0 7/8
M20x1.5 20.0 1.50 18.5 47/64 22.0 7/8
M22x2.5 22.0 2.50 19.5 49/64 25.0 1
M22x1.5 22.0 1.50 20.5 13/16 25.0 1
M24x3 24.0 3.00 21.0 53/64 27.0 1-5/64
M24x2 24.0 2.00 22.0 7/8 27.0 1-5/64
M27x3 27.0 3.00 24.0 15/16 30.0 1-3/16
M27x2 27.0 2.0 25.0 1 30.0 1-3/16

Standard UNC Tap Drill Sizes
Standard UNF Tap Drill Sizes
Standard NPT Tap Drill Sizes

Unified Screw Threads – Fine (UNF)

Unified Screw Threads – Fine are the most common type of fine thread found in the US.  Fine threads are useful for imparting a higher tensile load to the bolt with lower assembly torque required.  Unified screw threads consist of a 60-degree thread profile.

The table below shows the major and minor diameters, thread pitch (given in threads per inch, tpi) and finally the diameter  area which is necessary for bolt tensile strength calculations.


Size Major Dia Threads Per Inch Pitch Dia Minor Dia External Minor Dia Internal Minor Dia Area Tensile Stress Area
# inch tpi inch inch inch sq. inch sq. inch
#0 0.06 80 0.0519 0.0451 0.0465 0.00151 0.0018
#1 0.073 72 0.064 0.0565 0.058 0.00237 0.00278
#2 0.086 64 0.0759 0.0674 0.0691 0.00339 0.00394
#3 0.099 56 0.0874 0.0778 0.0797 0.00451 0.00523
#4 0.112 48 0.0985 0.0871 0.0894 0.00566 0.00661
#5 0.125 44 0.1102 0.0979 0.1004 0.00716 0.0083
#6 0.138 40 0.1218 0.1082 0.1109 0.00874 0.01015
#8 0.164 36 0.146 0.1309 0.1339 0.01285 0.01474
#10 0.19 32 0.1697 0.1528 0.1562 0.0175 0.02
#12 0.216 28 0.1928 0.1734 0.1773 0.0226 0.0258
1/4 0.25 28 0.2268 0.2074 0.2113 0.0326 0.0364
5/16 0.3125 24 0.2854 0.2629 0.2674 0.0524 0.058
3/8 0.375 24 0.3479 0.3254 0.3299 0.0809 0.0878
7/16 0.4375 20 0.405 0.378 0.3834 0.109 0.1187
1/2 0.5 20 0.4675 0.4405 0.4459 0.1486 0.1599
9/16 0.5625 18 0.5264 0.4964 0.5024 0.189 0.203
5/8 0.625 18 0.5889 0.5589 0.5649 0.24 0.256
3/4 0.75 16 0.7094 0.6763 0.6823 0.351 0.373
7/8 0.875 14 0.8286 0.79 0.7977 0.48 0.509
1 1 12 0.9459 0.9001 0.9098 0.625 0.663
1-1/8 1.125 12 1.0709 1.0258 1.0348 0.812 0.856
1.25 12 1.1959 1.1508 1.1598 1.024 1.073
1-3/8 1.375 12 1.3209 1.2758 1.2848 1.26 1.315
1.5 12 1.4459 1.4008 1.4098 1.521 1.581

If you need a screw that is less sensitive to over-torquing, consider using a Unified Screw Thread – Course (UNC) instead of the Unified Screw Thread – Fine (UNF).

Unified Screw Threads – Course (UNC)

Unified Screw Threads – Course are the most common type of thread found in the US.  Unified screw threads consist of a 60-degree thread profile.

The table below shows the major and minor diameters, thread pitch (given in threads per inch, tpi) and finally the diameter  area which is necessary for bolt tensile strength calculations.


Size Major Dia Threads Per Inch Pitch Dia Minor Dia External Minor Dia Internal Minor Dia Area Tensile Stress Area
# inch tpi inch inch inch sq. inch sq. inch
#1 0.073 64 0.0629 0.0544 0.0561 0.00218 0.00263
#2 0.086 56 0.0744 0.0648 0.0667 0.0031 0.0037
#3 0.099 48 0.0855 0.0741 0.0764 0.00406 0.00487
#4 0.112 40 0.0958 0.0822 0.0849 0.00496 0.00604
#5 0.125 40 0.1088 0.0952 0.0979 0.00672 0.00796
#6 0.138 32 0.1177 0.1008 0.1042 0.00745 0.00909
#8 0.164 32 0.1437 0.1268 0.1302 0.01196 0.014
#10 0.19 24 0.1629 0.1404 0.1449 0.0145 0.0175
#12 0.216 24 0.1889 0.1664 0.1709 0.0206 0.0242
¼ 0.25 20 0.2175 0.1905 0.1959 0.0269 0.0318
5/16 0.3125 18 0.2764 0.2464 0.2524 0.0454 0.0524
3/8 0.375 16 0.3344 0.3005 0.3073 0.0678 0.0775
7/16 0.4375 14 0.3911 0.3525 0.3602 0.0933 0.1063
½ 0.5 13 0.45 0.4084 0.4167 0.1257 0.1419
9/16 0.5625 12 0.5084 0.4633 0.4723 0.162 0.182
5/8 0.625 11 0.566 0.5168 0.5266 0.202 0.226
¾ 0.75 10 0.685 0.6309 0.6417 0.302 0.334
7/8 0.875 9 0.8028 0.7427 0.7547 0.419 0.462
1 1 8 0.9188 0.8512 0.8647 0.551 0.606
1-1/8 1.125 7 1.0322 0.9549 0.9704 0.693 0.763
1.25 7 1.1572 1.0799 1.0954 0.89 0.969
1-3/8 1.375 6 1.2667 1.1766 1.1946 1.054 1.155
1.5 6 1.3917 1.3016 1.3196 1.294 1.405
1.75 5 1.6201 1.5119 1.5335 1.74 1.9
2 2 4.5 1.8557 1.7353 1.7594 2.3 2.5
2.25 4.5 2.1057 1.9853 2.0094 3.02 3.25
2.5 4 2.3376 2.2023 2.2294 3.72 4
2.75 4 2.5876 2.4523 2.4794 4.62 4.93
3 3 4 2.8376 2.7023 2.7294 5.62 5.97
3.25 4 3.0876 2.9523 2.9794 6.72 7.1
3.5 4 3.3376 3.2023 3.2294 7.92 8.33
3.75 4 3.5876 3.4523 3.4794 9.21 9.66
4 4 4 3.8376 3.7023 3.7294 10.61 11.08

If you need to apply more tensile load with less torque, consider using a Unified Screw Thread – Fine (UNF) instead of the Unified Screw Thread – Course (UNC).