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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.

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Galvanic Corrosion and the Compatibility of Metals – Anodic Index

Designs sometimes cause dissimilar metals to be in contact within an assembly.  Increased variance of the two metals’ anodic index cause accelerated corrosion of the more anodic metal.  This is called galvanic corrosion.  The variance in anodic index can be controlled somewhat through coatings (paint, epoxy, powder coat, etc) and plating (zinc, chrome, etc).

The table below provides a generalize guide for predicting the anodic corrosion two dissimilar metals are prone to.  The service environment also plays a role:

  • For harsh environments: outdoors, high humidity, and salt environments fall into this category. Typically there should be not more than 0.15 V difference in the “Anodic Index”. For example; gold – silver would have a difference of 0.15V being acceptable.
  • For normal environments: storage in warehouses or non-temperature and humidity controlled environments. Typically there should not be more than 0.25 V difference in the “Anodic Index”.
  • For controlled environments: where the temperature and humidity controlled, 0.50 V can be tolerated. Caution should be maintained when deciding for this application as humidity and temperature do vary from regions.

Anodic Index

Metallurgy Index (V)
Gold, solid and plated, Gold-platinum alloy 0.00
Rhodium plated on silver-plated copper 0.05
Silver, solid or plated; monel metal. High nickel-copper alloys 0.15
Nickel, solid or plated, titanium an s alloys, Monel 0.30
Copper, solid or plated; low brasses or bronzes; silver solder; German silvery high copper-nickel alloys; nickel-chromium alloys 0.35
Brass and bronzes 0.40
High brasses and bronzes 0.45
18% chromium type corrosion-resistant steels 0.50
Chromium plated; tin plated; 12% chromium type corrosion-resistant steels 0.60
Tin-plate; tin-lead solder 0.65
Lead, solid or plated; high lead alloys 0.70
Aluminum, wrought alloys of the 2000 Series 0.75
Iron, wrought, gray or malleable, plain carbon and low alloy steels 0.85
Aluminum, wrought alloys other than 2000 Series aluminum, cast alloys of the silicon type 0.90
Aluminum, cast alloys other than silicon type, cadmium, plated and chromate 0.95
Hot-dip-zinc plate; galvanized steel 1.20
Zinc, wrought; zinc-base die-casting alloys; zinc plated 1.25
Magnesium & magnesium-base alloys, cast or wrought 1.75
Beryllium 1.85
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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
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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

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Tap Drill Size – UNF

Below is a table of drill and tap sizes for Unified Screw Threads – Fine, UNF.

UNF screws may not always be appropriate.  Depending on the application, you may be better off using UNC fasteners.


INCH SIZES – NATIONAL FINE
TAP SIZE DRILL SIZE
#1-72 #53
#2-64 #50
#3-56 #46
#4-48 #42
#5-44 #37
#6-40 #33
#8-36 #29
#10-32 #21
#12-28 #15
1/4-28 #3
5/16-24 I
3/8-24 Q
7/16-20 W
1/2-20 29/64
9/16-18 33/64
5/8-18 37/64
3/4-16 11/16
7/8-14 13/16
1″-12 15/16
1-1/8-12 1-3/64
1-1/4-12 1-11/64
1-1/2-12 1-27/64
1-3/4-12 1-43/64
2″-12 1-59/64

Metric Tap Drill Sizes
Standard UNC Tap Drill Sizes
Standard NPT Tap Drill Sizes

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Tap Drill Size – UNC

Below is a table of drill and tap sizes for Unified Screw Threads – Course, UNC.

UNC screws may not always be appropriate.  Depending on the application, you may be better off using UNF fasteners.


INCH SIZES – NATIONAL COARSE
TAP SIZE DRILL SIZE
#0-80 3/64″
#1-64 #53
#2-56 #51
#3-48 5/64″
#4-40 #43
#5-40 #39
#6-32 #36
#8-32 #29
#10-24 #25
#12-24 #17
1/4-20 #7
5/16-18 F
3/8-16 5/16
7/16-14 U
1/2-13 27/64
9/16-12 31/64
5/8-11 17/32
3/4-10 21/32
7/8-9 49/64
1″-8 7/8
1-1/8-7 63/64
1-1/4-7 1-7/64
1-1/2-6 1-11/32
1-3/4-5 1-35/64
2″-4-1/2 1-25/32

Metric Tap Drill Sizes
Standard UNF Tap Drill Sizes
Standard NPT Tap Drill Sizes

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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
1¼ 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
1½ 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).