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Grade Markings:

Other Grade markings at AmericanFastener.com
(Note: Metric class [e.g. 8.8] is different than SAE grade. Class 8.8 is grade 5.)

Bolt Class and Grade (Torque specs vary - numbers below are at high end.)
TypeMaterial Tensile
Torque ft-lbs. e.g. *
size-pitch (tpi)
   C.P. 50Titanium50,000     
  2024-T4 cold-formed Aluminum262,000   6-9 
ASTM 302 Stainless Steel1102,000     
 18-8304 Stainless Steel102,000 -6-20-22-45
A4-80316316 Stainless Steel116,000 7212347
5.82  Low Carbon Steel74,000 4-6 16-21 22-24 52-63
6.83 Med Carbon Steel     
8.8 5  Med Carbon Heat T. Steel120,000 8-10 30-37 35-42 90-101
   ASME B16 CrMoVa Alloy Steel125,000        
   8740 chrome moly180,000        
  5  high tensile Titanium120,000
9.8 6-7  Med. Carbon Temp. Steel133,000 10-40-45-100-
10.9 8  Med. Carbon Alloy Temp. Steel150,000 12-14 45-52 50-59 120-144
12.9    Alloy Temp. Steel170,000
  "Stainless 300" Stainless Steel special alloy from ARP170,000     
  416-HT Stainless Steel180,000     
    Aermet 100steel super-alloy3 300,000
psi - Pounds per square inch
tpi - Threads per inch
C.P. - Commerciallly Pure
HT - Hardened and Tempered
Temp. - Quenched and Tempered
See other terms below
† - Strength: pounds per square inch (psi)(English unit) or in Megapascal (MPa) (SI unit)
MPa - Megapascal = 1 N/mm2 = 145 psi
Standard Fastener Rated
Yield (Proof) Strengths
SAE Grade 5 586 MPa 85,000 psi
SAE Grade 8 527 MPa 120,000 psi
ISO Class 5.8 380 MPa
ISO Class 8.8 580 MPa
ISO Class 10.9 830 MPa
ISO Class 12.9 970 MPa
Metric ISO Class:
The number before the point is the ultimate tensile strength in MPa divided by 100. The number after the point is 10 times the ratio of tensile yield strength to ultimate tensile strength. For example, a property class 5.8 bolt has a nominal (minimum) ultimate tensile strength of 500 MPa, and a tensile yield strength of 0.8 times ultimate tensile strength or 0.8(500) = 400 MPa.
See table below.
Metric System & Specifications.pdf | fastenal.com


Property Class Designation Nominal Size of Product Material and Treatment Mechanical Requirements Property Class Ident. Marking
Proof Load Stress, MPa Tensile Yield Strength, MPa, Min. Tensile Ultimate Strength, MPa, Min. Prod. Hardness, Rockwell
Surface, Max. Core
Min. Max.
4.6 M5-M100 low or medium carbon steel 225 240 400 -- B67 B95 4.6
4.8 M1.6-M16 low or medium carbon steel, fully or partially annealed 310 340 420 -- B71 B95 4.8
5.8 M5-M24 low or medium carbon steel, cold worked 380 420 520 -- B82 B95 5.8
8.8 M16-M72 medium carbon steel, quenched and tempered 600 660 830 30N56 C23 C34 8.8
A325M Type 1 M16-M36 A325M  8S
8.8 M16-M36 low carbon boron steel, quenched and tempered 600 660 830 30N56 C23 C34 8.8
A325M Type 2 A325M  8S
A325M Type 3 M16-M36 atmospheric corrosion resistant steel, quenched and tempered 600 660 830 30N56 C23 C34 A325M  8S3
9.8 M1.6-M16 medium carbon steel, quenched and tempered 650 720 900 30N58 C27 C36 9.8
9.8 M1.6-M16 low carbon boron steel, quenched and tempered 650 720 900 30N58 C27 C36 9.8
10.9 M5-M20 medium carbon steel, quenched and tempered 830 940 1040 30N59 C33 C39 10.9
10.9 M5-M100 medium carbon alloy steel, quenched and tempered 830 940 1040 30N59 C33 C39 10.9
A490M Type 1 M12-M36 A490M  10S
10.9 M5-M36 low carbon boron steel, quenched and tempered 830 940 1040 30N59 C33 C39 10.9
A490M Type 2 M12-M36 A490M  10S
A490M Type 3 M12-M36 atmospheric corrosion resistant steel, quenched and tempered 830 940 1040 30N59 C33 C39 A490M  10S3
12.9 M1.6-M100 alloy steel, quenched and tempered 970 1100 1220 30N63 C38 C44 12.9
Return to Structural Analysis Reference Library. © 2003 Garrett D. Euler
The number before the point is the ultimate tensile strength in MPa divided by 100. The number after the point is 10 times the ratio of tensile yield strength to ultimate tensile strength. For example, a property class 5.8 bolt has a nominal (minimum) ultimate tensile strength of 500 MPa, and a tensile yield strength of 0.8 times ultimate tensile strength or 0.8(500) = 400 MPa.
Caution is advised when considering the use of property class 12.9 products. The capabilities of the fastener manufacturer, as well as the anticipated service environment, should be carefully considered. Some environments may cause stress corrosion cracking of nonplated, as well as electroplated, products.
In the United States, property classes 8.8.3 and 10.9.3 also defined; the "3" after the second decimal point indicates the fastener is made of weathering steel.
* Torques are examples. Coatings like crome, cadmium or zinc and lubricants, inculding Loctite (which acts as a lubricant before it dries) will affect the torque required. (higher numbers in above chart are for zinc plated bolts). Torque tables will vary by 10-15%. The MIL-Specs (NAS and MS) are used by the aircraft industry. The above numbers tend to be toward the high end of the ranges. See Torque below for more information and links to torque tables.

In the 1980's large numbers of counterfeit bolts appeared in the United States, almost all imports. For this reason, the SAE grade markings can no longer be trusted unless one knows exactly who made and graded the bolt.

A stronger bolt may not always be better. In some cases a bolt may be selected to fail at a certain stress to protect a more expensive part.

Bolts are graded, designating how "hard" they are. The "harder" bolt you choose, the higher the grade number, and the more brittle or "less shear resistant" it becomes. Higher grades are not necessairly better depending on the use.
The bolt material strength is determined by the alloy and processing method (for example, cold working and heat treating.)

The American Society for Testing Materials (ASTM) is one of the organizations which grades fastners in specification documents e.g. A193, A194, A320. Some equivalent grades are:
ASTM Title
A193 Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for High-Temperature Service.
A194 Standard Specification for Carbon and Alloy Steel Nuts for Bolts for High Pressure or High Temperature Service, or Both
A307 Standard Specification for Carbon Steel Bolts and Studs, 60 000 PSI Tensile Strength
A320 Standard Specification for Alloy-Steel and Stainless Steel Bolting Materials for Low-Temperature Service
Grade ASTM Description
B7 A193 A heat-treated chromium-molybdenum steel widely used for medium high temperature service.
B8 A193 These Chromium-Nickel (AISI 304) austenitic steel studs are used in corrosive environments (-325* to 1500*F).
B8M A193 These Chromium-Nickel Molybdenum (AISI 316) austenitic steel studs are used in corrosive environments (-325* to 1500*F)
L7 A320 Intended for low temperature service down to minus 150* and has a minimum Charpy impact value of 20 ft lb at this temperature (-150* to 1100*F)
L7 A194 Heat-treated chrome-molybdenum steel nuts suitable for extreme temperature and pressure conditions.
18-8 Stainless Steel This is the most popular type of stainless used in the production of fasteners. Its composition is approximately 18% Chromium and 8% Nickel, thus the name 18-8. Several grades of stainless are included in this classification including 302, 303, 304 and 305. These all have good strength and corrosion resistance.

316 Stainless Steel This is more corrosion resistant than 18-8, but also more expensive. It is composed of approximately 18% Chromium and 12% Nickel with the addition of 2% to 4% Molybdenum. It also maintains its strength at higher temperatures than 18-8.

410 Stainless Steel It has approximately 12% Chromium with no Nickel. It is not very corrosion resistant and is magnetic, but it can be heat treated to become harder.

Alloy 20 This alloy has approximately 20% Chromium and 34% Nickel plus 3% to 4% Molybdenum. It is very corrosion resistant and is especially popular when in contact with sulfuric acid.

Brass This metal is approximately 65% Copper and 35% Zinc. It offers a good combination of strength, corrosion resistance and workability.

Nickel Copper 400 This alloy is approximately 70% Nickel and 30% Copper. It has excellent strength and corrosion resistance and is used in salt water marine and other chemical environments.

Titanium This has a very high strength to weight ratio, as well as good corrosion resistance.

Inconel Registered Trademark of Inco Ltd. Composed of approximately 77% Nickel and 15% Chromium. It offers superior strength and good corrosion at high temperatures.

Silicon Bronze It is composed of approximately 96% Copper, 3% Silicon, and 1% Manganese. It is more corrosion resistant and tougher than brass. It is widely used in the electrical industry.

ISO metric fastener material strength property classes (grades) is specified in ISO Standard 898-1. The 5 in 5.8 means nominal (minimum) tensile ultimate strength is 5 * 100 = 500 MPa (Megapascal); the 8 means the yield strength is 0.8 times tensile ultimate strength or 0.8 * 500 = 400 MPa.

1. - Stainless Steel Tensil strength ranges from 74,000 - 180,000 psi.
There are two common types of stainless steel fasteners: corrosion-resistant stainless steel, ASTM 304 (a.k.a. 18-8 †) or DIN/ISO A2, and acid-resistant stainless steel, ASTM 316 or DIN/ISO A4. A2 is by far the most prevalent material, and is what is normally supplied for stainless metric fasteners.

† - 18-8 or 18/8 - Means that it contains 18% chromium and 8% nickel. A better grade is 18/10 it provides more corrosion resistance and greater durability.

There are three typical property classes (strengths) for in the metric system: 50, 70, and 80. The class equals the tensile strength divided by 10. The metric property class is a dash (-) number after the alloy designator. For example, a screw marked A2-70 is a 304 stainless steel screw with a 700 N/mm2 tensile strength. Both alloys come in all property classes, but A2-70 and A4-80 are the most common.

304 316 384 Austenitic Stainless Steel, Cold Worked
416-HT - Martensitic Stainless Steel Hardened and Tempered

316 stainless steel is a higher alloyed material containing 2-3% molybdenum, which provides improved pitting and crevice corrosion resistant properties, especially in environments containing chlorides.

2. Aluminum 1024-T4 - 1024 specifies Alloy per Aluminum Association series and T4 the temper.
T4 = Solution heat treated and naturally aged to a substantially stable condition.
See: Aluminum Tempers at EngineersEdge.com
Aluminum Alloys
Typical mechanical properties of wrought aluminum alloys
Composition of Aluminum 2XXX Series Alloys

3. AERMET 100 is a martensitic steel super-alloy from ARP that is used for conecting rod bolts in top fuel dragsters.

See Fasteners

Terms: (See also standards below)
12N - National 12 Pitch
304SS = 304 Stainless Steel
5000SA = 5000 Series Aluminum
ASTM - American Society for Testing and Materials
AHSS - Advanced High-Strength Steels
ARP - Automotive Racing Products
C.P. - Commerciallly Pure
DP - Dual phase steel - Comprised of soft ferrite and, depending on strength, between 20 and 70% volume of hard phases, normally martensite.
FT - Fine thread (same as UNF)
FH - Flat Head
HH - Hex Head
HSLA - High-strength, low alloy steel
HSS = High Strength Steel
HT - Hardened and Tempered Quenching and tempering - A process that is heating to about 900°C, water quenching, and tempering at temperatures of 480 to 600°C or higher, can provide a tempered martensitic or bainitic microstructure that results in better combinations of strength and toughness. An increase in the carbon content to about 0.5%, usually accompanied by an increase in manganese, allows the steels to be used in the quenched and tempered condition.Martensitic - A DP steel with Ferrite + Martensite; Martensite is a highly supersaturated solid solution of carbon in iron (iron carbide).
It is formed when steel is cooled so rapidly that the change from austenite to pearlite is suppressed.
HX - Hex Head
LCS = Low Carbon Steel
Martensitic steel has a much higher ultimate tensile strength than conventional steels of similar yield strength.
MIL - Military Spec Numbers (see MS, NAS below)
NC - National Coarse thread pitch (same as UNC)
MPa - Megapascal = 1 N/mm2 = 145 psi
NF - National Fine thread pitch (same as UNF)
NEF - National Extra Fine thread pitch
Nm - Newton meter = 0.75 ft lb
N/mm2 - Newtons per square millimeter.
    1 N/mm2 = 145.03 pounds/in2 (psi) = 1 MPa
NS - National Special thread pitch
OH - Oval Head
PH - Pan Head
PH - Phillips Drive
psi - Pounds per square inch p/in2.
Rm - Ultimate tensile strength - The tensile strength (ultimate) strength, is the stress level where the material breaks under tension (Trying to stretch it out).

RP0,2 - yield strength or proof strength -
RP0.2 or RP0,2 is the amount of stress that will result in a plastic strain of 0.2%.
SI - International System of Units SL - Slotted Drive
SHCS - Socket Head Cap Screw
Temp. - Quenched and Tempered
Tensil Strength - see Rm above
TRIP - Transformation Induced Plasticity Streel
tpi - Threads per inch
UNC - Unified National Course thread form
Unified National Fine thread series or just "Fine Thread (FT)"
Yield Strength - See RP0.2 above

See: High-Strength Structural and High-Strength Low-Alloy Steels

ISO - International Organization for Standardization - ISO 898-1, 1999
SAE - Society of Automotive Engineers - SAE J429
ASTM - American Society for Testing Materials
AISI - American Iron and Steel Institute.
ASME - American Society of Mechanical Engineers
COFS - Committee on Framing Standards of AISI
AA - Aluminum Association Defines series (1000, 2000, ...) of Aluminum Alloys
MIL-spec - Military Specifications (AN, NAS, MS, ..)
  DLA Defense Logistics Agency
  AN - Army/Navy or Air Force/Navy - World War II era hardware standards.
  NAS - National Aerospace Standards. Korea era standards systems now almost totally duplicated by the MS system. Aerospace Fasteners List at SPS Technologies
  MS - Military Standard specification. Cold war era standards required as airplanes got more complicated.
  Unfortunately, this numbering system lacks much of the logic of the AN system it replaces. Dash numbers vary from part number to part number and seems to bear no resemblance to size.
DIN - Deutsches Institut fur Normung (German Standards Institute). (usually uses same nomenclature/specs. as ISO)

See Glossaries at: bonaero.com, Defense Logistics Agency

Torque Notes:
A properly tightened bolt is one that is stretched such that it acts like a very ridged spring pulling mating surfaces together. There are no standard tables, because tightening is not an accurate science.
Guidelines for Torque:

  • Torque for lubricated bolts should be about 30% fo 50% less than the unlubricated values above.
  • Loctite® acts as a mild lubricant before it drys. Use about 15% less torque.
  • Cadmium plating - 25-30% less
  • Zinc plating - 10-40% more. (higher numbers in above chart are for zinc plated)
  • Stainless steel fasteners have a friction coefficient about two times the corresponding plain steel fastener. This does not mean that stainless fasteners require double the specified torque since they usually cannot achieve the strength of a steel fastener.
  • Super clean fasteners or those lubricated with light lubricants like WD-40™ require a high torque to achieve the desired tension.
  • Fasteners lubricated with oil such as motor oil and the oil found on black fasteners require a medium torque.
  • Fasteners lubricated with extreme pressure grease or anti-seize paste require the least torque.
  • For bolts in shear reduce the values by 30-40%.
  • Loctite is preferred over lockwashers because lockwashers decrease bolt clamping efficiency and Loctite serves initially as a lubricant.
  • Always "feel" for tightness even when using a torque wrench.
  • Try to avoid button head Allen/Torx bolts where any sort of torque is required. They simply round out.
  • As a rule, when a bolt is installed, the nut (over a washer) should be turned and not the bolt's head.
  • Unless a torque wrench is used the tendency is to undertighten large bolts and overtighten small ones.
Bolt Torque by Grade at: Rask Cycle, MetTec, ZeroFast.com, dansmc.com, sizes.com/tools/bolts_SAEtork.htm
Torque and Fastener Matching Information (NAS torques) at Costal Fabrication.
Keeping it All Together - The Nuts and Bolts of Bolting
Marine Fastners.

Recommended Torque Spec's for Titanium Fasteners
Torque and Screw Interchangeability at Bondhus.

Preloading accuracy
Method By Feel Torque Wrench Turn-of-nut Preload washers Bolt elongation Strain gauges
Accurcy +/- 35% +/- 25% +/- 15% +/- 10% +/- 3% +/- 1%
Source: the "Machinery's Handbook".

Sliding friction is affected by materials (like steel or aluminum on titanium), surface roughness, bearing area, material hardness, lubrication and so on. It takes more force to tighten a larger bolt. It takes more force to stretch an SAE Grade 8 bolt than it does to stretch an SAE Grade 5 bolt because of the greater material strength.

Undertorque can result in unnecessary wear of nuts and bolts as well as the parts they hold together. When insufficient pressures are applied, uneven loads will be transmitted throughout the assembly which may result in excessive wear or premature failure due to fatigue.
Overtorque can be equally damaging because of failure of the bolt or nut from overstressing the thread areas.

The basic formula Torque = K x D x P where:
K - Coefficient of friction (nut factor). The most commonly used bolting K factors arc 0.20 for plain finished bolts, 0.22 for zinc plated bolts, and 0.10 for waxed or highly lubricated bolts.
D - Bolts nominal diameter (in. for in-lbs. or ft. for ft -lbs)
P = Bolt's desired tensile load in pounds (generally 75% of yield strength - the stress level where the material yields or permanently deforms.)
Source: ZeroFast.com

Bolt Sizes (inch/SAE to Metric) TPI = Threads per inch

Size Conversion
in. mm.
1/8 3.18
5/32 3.97
3/16 4.76
7/32 5.55
1/4 6.35
9/32 7.14
5/16 7.94
3/8 9.52
7/16 11.11
1/2 12.70
9/16 14.29
5/8 15.88
11/16 17.46
3/4 19.05
13/16 20.6
See Tap sizes. and Screw Sizes
Size Dec. mm. TPI
Size Dec. mm. TPI
#0 0.06 1.52 80
#1 0.073 1.85 64 72
#2 0.086 2.18 56 64
#3 0.099 2.51 48 56
#4 0.112 2.84 40 48
#4 0.112 2.84 36
#5 (1/8) 0.125 3.18 40 44
#6 0.138 3.51 32 40
5/32 0.156 3.97 32
#8 0.164 4.17 32 36
3/16 0.187 4.76 24
#10 0.19 4.83 24 32
#12 0.216 5.49 24 28
7/32 0.219 5.55 24
#14 0.242 6.15 20 24
Size Dec. mm. TPI
1/4 0.25 6.35 20 28 32
5/16 0.3137.9418 24
3/8 0.3759.5216 24
7/16 0.438 11.1114 20 28
1/2 0.5012.7013 20 28
9/16 0.563 14.2912 18 24
5/8 0.62515.8811 18 24
3/4 .75= 19.0510 16
Threads per inch (tpi) Thread Series
National Coarse (NC), National Fine (NF), National Extra Fine (NEF), National Special (NS), National 12 Pitch (12N)
Note: Pipe threads use different sizing. Some of the tubes and lines in cars use pipe thread sizes. See pipes.

Tap Drill Sizes
See Tap Drill Size page.

Drill Sizes:
See Drill size Page.

Wrench Sizes:
Hex Head wrench sizes
Allen wrench (Hollow Set Screw) sizes


  • The number before the decimal point is one-hundredth of the nominal tensile strength of the bolt in newtons per square millimeter.
  • The number after the decimal point is the ratio between the nominal yield stress and the nominal tensile strength, times ten.
8.8 is the standard automotive grade with a tensile strength of approx 120,000psi.
Inch Grade Marks on Head Material Tensile Strength Yield Strength
N/mm2 psi N/mm2 psi
2 none Low Carbon Steel 510 74,000 393 57,000
5 3 Med. Carbon Heat T. Steel 827 120,000 634 92,000
8 6 Alloy Steel 1030 150,000 896 130,000
SHCS none Alloy Steel 1240 180,000 965 140,000
18-8 none 302 Stainless 690 100,000 448 65,000
316 none 316 Stainless 690 100,000 448 65,000

Metric Class Marks on Head Material Tensile Strength Yield Strength
N/mm2 psi N/mm2 psi
8.8 8.8 Steel 800 116,000 640 93,000
10.9 10.9 Steel 1040 151,000 940 136,000
12.9 12.9 Alloy Steel 1220 177,000 1100 160,000
A2-70 A2-70 302 Stainless 700 102,000 450 65,000
A4-80 A4-80 316 Stainless 800 116,000 600 87,000
Source: "The Nuts and Bolts of Bolting" by Joseph C. Dille

I found a discussion on a message board where there was no agreement on when to lubricate. Some thought you should always oil a bolt to make it easier to remove and another thought it would make it too easy to loosen.
When using chromed or stainless-steel fasteners, is the appropriate use of Anti-Seize to avoid galling and binding of the bolts when tightening (see Permatex Loctite tech).

US & Metric Bolt Torque by Grade
Screw Finder at BobbyDyer.com
Technical Reference Guide | Fastenal.com
Metric Bolt Properties, Grades, and Strength
Organizing Nuts, Bolts and Washers - Addtoit
Screw Information at search.com
Screwtypes at lara.com
Fastener Material Chart at CenturyPerformance.com
Metric Bolt Properties Grade, Strength
Shear force - Wikipedia, the free encyclopedia
Proof Loads at FullerMetric.com
Strength at AtlanticFasteners.com
ASTM, SAE AND ISO grade markings and mechanical properties for steel fasteners at AmericanFastener.com
SAE Standards for Bolts
CD Stud Fasteners Specifications at SunBeltWelding
Tap Drill Sizes
Corrosion Resistant Bolts at contractors-sources.com
Aircraft Hardware
Automotive Racing Products (ARP)- Bolts
Stainles Steel fasteners with specs for Aluminum, Titanium also at ssina.com
Fastener and Screw / Bolt Design, Formula and Calculation at Engineers Edge
Strength Properties of Metals at EngineersEdge.com
The Tempering of Martensite
Types of bolts and screw heads.
Fastener types.
Fasteners 101
Home Depot Special Order Fasteners at CrownBolt.com

"The Nuts and Bolts of Bolting" by Joseph C. Dille
Fastners 101
Bolted Connections | Michigan State CE 405
Metallurgy for the Non-Engineer

Gardner-Westcott is a bolt manufacturer.
High Quality Machine Screws, Hex Head Bolts and Nuts Cheap from SwapMeetDave.com

Pozidriv™ is a trademark of European Industrial Services Ltd.
Pozidriv® is a registered trademarks of Phillips Screw Co.
Torx® is a reg. trademark of Camcar-Textron Inc. USA

last updated 7 Sep 2013