Grade Markings:

Other Grade markings at AmericanFastener.com

Bolt Class and Grade (Torque specs vary - numbers below are at high end.)

Metric Class ISO	Inch Grade SAE	Type	Material	Tensile Strength (psi)	Torque ft-lbs. e.g. * size-pitch (tpi)
					¼-20	3/8-16 (10mm.)	3/8-24	½-20
3.6
4.6
4.8
		C.P. 50	Titanium	50,000
		2024-T4	cold-formed Aluminum2	62,000			6-9
			SBrass	70,000
A2-70	18-8	ASTM 302	Stainless Steel1	102,000
	18-8	304	Stainless Steel	102,000	-6	-20	-22	-45
A4-80	316	316	Stainless Steel	116,000	7	21	23	47
5.8	2		Low Carbon Steel	74,000	4-6	16-21	22-24	52-63
6.8	3		Med Carbon Steel
8.8	5		Med Carbon Heat T. Steel	120,000	8-10	30-37	35-42	90-101
		ASME B16	CrMoVa Alloy Steel	125,000
		8740	chrome moly	180,000
	5		high tensile Titanium	120,000 160,000		13-15	17-21	64-79
9.8	6-7		Med. Carbon Temp. Steel	133,000	10-	40-	45-	100-
10.9	8		Med. Carbon Alloy Temp. Steel	150,000	12-14	45-52	50-59	120-144
12.9			Alloy Temp. Steel	170,000
		"Stainless 300"	Stainless Steel special alloy from ARP	170,000
		416-HT	Stainless Steel	180,000
		Aermet 100	steel 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

* 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.

MATERIALS
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.

† - 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.

Type:
See Fasteners

Terms: (See also standards below)
12N - National 12 Pitch
304SS = 304 Stainless Steel
5000SA = 5000 Series Aluminum
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)
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
NS - National Special thread pitch
OH - Oval Head
PH - Pan Head
PH - Phillips Drive
psi - Pounds per square inch.
Rm - Ultimate tensile strength - The tensile strength (ultimate) strength, is the stress level where the material breaks under tension (Trying to stretch it out).

R_P0.2 - yield strength - The yield strength is the stress level where the material yields or permanently deforms.
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
MPa - Megapascal = 1 N/mm² = 145 psi
UNC - Unified National Course thread form
Unified National Fine thread series or just "Fine Thread (FT)"
Yield Strength - See R_P0.2 above

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

Standards:
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.

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)

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

Metric:

• 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.

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

Lubrication:
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).

"The Nuts and Bolts of Bolting" by Joseph C. Dille
Fastners 101
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