Bolt Head Marking Chart

Identification Grade Mark	Specifications	Material	Normal Size Dia. In	Proof Load PSI (Mpa)	Tensile Strength Min. PSI (Mpa)	Yield Strength Min. PSI	Bolt Rockwell Hardness		Nut Rockwell Hardness
							Min	Max	Min	Max
	SAE J429 Grade 1	Low Carbon Steel	1/4″ – 1 1/4″	33.000	60.000	36,000	B70	B100
	SAE J429 Grade 2		1/4 ” –  3/4″ 3/4″ – 1 1/2″	55.000 33.000	60.000 74.000	57.000 36.000	B80	B100		C32
	Property Class 5.8	Low or Medium Carbon Steel	M5 – M24	55.100 (380)	75.400 (520)		B82	B95		C32
	SAE J429 Grade 5	Medium Carbon Steel, Quenched and Tempered	1/4 – 1 1″ – 1-1/2″	85,000 74,000	120,000 105,000	92,000 81,000	C25 C19	C34 C30		C32
	ASTM A449		1/4″ – 1″ 1″ – 1-1/2 1-1/2″ – 3″	85,000 74,000 55,000	120,000 105,000 90,000	92,000 81,000 58,000
	SAE J429 Grade 5.1	Low or Medium Carbon Steel, Quenched and Tempered	No. 6 thru 3/8	85,000	120,000		C25	C40
	SAE J429 Grade 5.2	Low Carbon Martensitic Steel, Quenched and Tempered	1/4 thru 1	85,000	120,000	92,000
	ASTM A325 Type 1	Medium Carbon Steel, Quenched and Tempered	1/2 thru 1 1-1/8 thru 1-1/2	85,000 74,000	120,000 105,000	92,000 81,000
A325	ASTM A325 Type 2	Low Carbon Martensitic Steel, Quenched and Tempered	1/2 thru 1	85,000	120,000	92,000
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	120,000 105,000	92,000 81,000
Identification Grade Mark	Specifications	Material	Normal Size Dia. In	Proof Load PSI (Mpa)	Tensile Strength Min. PSI (Mpa)	Yield Strength Min. PSI	Bolt Rockwell Hardness		Nut Rockwell Hardness
							Min	Max	Min	Max
BB	ASTM A354 Grade BB	Alloy Steel, Quenched and Tempered	1/4 thru 2-1/2 2-3/4 thru 4	80,000 75,000	105,000 100,000	83,000 78,000
BC	ASTM A354 Grade BC			105,000 95,000	125,000 115,000	109,000 99,000
	Property Class 9.8	Medium carbon steel, Quenched & tempered	M1.6 – M16	94.250 (650)	130.500 (900)		C27	C36		C32
	SAE J429 Grade 7	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 thru 1-1/2	105,000	133,000	115,000
	SAE J429 Grade 8	Medium Carbon Alloy Steel, Quenched and Tempered	1/4 thru 1-1/2	120,000	150,000	130,000
	ASTM A354 Grade BD	Alloy Steel, Quenched and Tempered
No Grade Mark	SAE J429 Grade 8.1	Medium Carbon Alloy or SAE 1041 Modified Elevated Temperature Drawn Steel	1/4 thru 1-1/2	120,000	150,000	130,000
	SAE Grade 8.2	Low carbon boron martensite steel fully killed fine grain quenched & tempered	1/4″ – 1″	120.000	150.000		C35	C42
Identification Grade Mark	Specifications	Material	Normal Size Dia. In	Proof Load PSI (Mpa)	Tensile Strength Min. PSI (Mpa)	Yield Strength Min. PSI	Bolt Rockwell Hardness		Nut Rockwell Hardness
							Min	Max	Min	Max
A490	ASTM A490	Alloy Steel, Quenched and Tempered	1/2 thru 1-1/2	120,000	150,000 min 170,000 max	130,000
No Grade Mark	ISO R898 Class 4.6	Medium Carbon Steel, Quenched and Tempered	All Sizes thru 1-1/2	33,000	60,000	36,000
No Grade Mark	ISO R898 Class 5.8			55,000	74,000	57,000
8.8 or 88	ISO R898 Class 8.8	Alloy Steel, Quenched and Tempered	All Sizes thru 1-1/2	85,000	120,000	92,000
10.9 or 109	ISO R898 Class 10.9	Alloy Steel, Quenched and Tempered	All Sizes thru 1-1/2	120,000	150,000	130,000
	Property Class 10.9	Medium carbon alloy steel quenched & tempered	M6 – M36	120.350 (830)	150.800 (1040)		C33	C39	C26	C36
	Property Class 12.9	Medium carbon alloy steel quenched & tempered	M1.6 – M36	140.000 (970)	176.900 (1220)		C38	C44	C26	C36

Mechanical
Mechanical Properties Of Fasteners

CLASS		New Designation	4.6	4.8	5.6	5.8	6.6	6.8	6.9	8.8	10.9	12.9	14.9
		Formerly	4D	4S	5D	5S	6D	6S	6G	8G	10K	12K	—
U.S. GRADE			1	2	2	2	3	3	3	5	8	—	—
Brinell		min. max.	110 170		140 215		170 245			225 300	280 365	330 425	390 —
Rockwell		min. max.	63 88		78 97		88 102			— —	— —	— —	— —
		min. max.								18 31	27 38	34 44	40 49
Yield Point psi			45,000		56,000		76,000		76,000	91,000	128,000	153,000	180,000
Tensile Strength psi		min. max.	56,000 78,000		70,000 100,000		85,000 113,000		85,338 99,561	113,784 128,000	142,230 170,676	170,000 200,000	200,000 230,000

Cap Screws
Hex Cap Screws

Nominal Or Basic Product Dia.	E		F			G		H			R	LT
	Body Diameter		Width Across Flats			Width Across Corners		Head Height			Radius of Fillet	Thread	Lngth.
												For Screw Lengths < 6 In.	For Screw Lengths > 6 In.
	Max.	Min.	Basic	Max.	Min.	Max.	Min.	Basic	Max.	Min	Min.	Basic	Basic
1/4 0.2500 5/16 0.3125 3/8 0.3750 7/16 0.4375	0.2500 0.3125 0.3750 0.4375	0.2450 0.3065 0.3690 0.4305	7/16 1/2 9/16 5/8	0.438 0.500 0.562 0.625	0.428 0.489 0.551 0.612	0.505 0.577 0.650 0.722	0.488 0.557 0.628 0.698	5/32 13/64 15/64 9/32	0.163 0.211 0.243 0.291	0.150 0.195 0.226 0.272	0.015 0.015 0.015 0.015	0.750 0.875 1.000 1.125	1.000 1.125 1.250 1.375
1/2 0.5000 9/16 0.5625 5/8 0.6250 3/4 0.7500	0.5000 0.5625 0.6250 0.7500	0.4930 0.5545 0.6170 0.7410	3/4 13/16 15/16 1-1/8	0.750 0.812 0.938 1.125	0.736 0.798 0.922 1.100	0.866 0.938 1.083 1.299	0.840 0.910 1.051 1.254	5/16 23/64 25/64 15/32	0.323 0.371 0.403 0.483	0.302 0.348 0.378 0.455	0.015 0.020 0.020 0.020	1.250 1.375 1.500 1.750	1.500 1.625 1.750 2.000
7/8 0.8750 1 1.0000 1-1/8 1.1250 1-1/4 1.250	0.8750 1.0000 1.1250 1.2500	0.8660 0.9900 1.1140 1.2390	1-5/16 1-1/2 1-11/16 1-7/8	1.312 1.500 1.688 1.875	1.285 1.469 1.631 1.812	1.516 1.732 1.949 2.165	1.465 1.675 1.859 2.066	35/64 39/64 11/16 25/32	0.563 0.627 0.718 0.813	0.531 0.591 0.658 0.749	0.040 0.060 0.060 0.060	2.000 2.250 2.500 2.750	2.250 2.500 2.750 3.000
1-3/8 1.3750 1-1/2 1.5000	1.3750 1.5000	1.3630 1.4880	2-1/6 2-1/4	2.062 2.250	1.994 2.175	2.382 2.598	2.273 2.480	27/32 15/16	0.878 0.974	0.810 0.902	0.060 0.060	3.000 3.250	3.250 3.500

Grade 8 Alloy
Reliant Frame Bolts Grade 8 Alloy

Nominal Size Or Basic Major Dia. Of Thread

E

F

G

B

U

H

LT

Body Dia.

Width Across Flats

Width Across Corners

Flange Dia.

Flange Thickness

Head Height

Thread Lngth.

L<6 In.

L>6 In.

Max.

Min.

Basic

Max.

Min.

Max.

Min.

Max.

Min.

Max.

Min.

Basic

3/8 0.3750 1/2 0.5000 5/8 0.6250 3/4 0.7500

0.3750 0.5000 0.6250 0.7500

0.3690 0.4930 0.6170 0.7410

9/16 3/4 15/16 1-1/8

0.5625 0.7500 0.9375 1.1250

0.551 0.736 0.922 1.100

0.650 0.866 1.083 1.299

0.618 0.825 1.034 1.234

0.81 1.07 1.33 1.59

0.06 0.08 0.10 0.11

0.39 0.51 0.62 0.73

0.25 0.34 0.42 0.51

1.000 1.250 1.500 1.750

1.250 1.500 1.750 2.000

 

Bolts are tools used to fasten and secure the faces of assemblies. They are threaded and come with a matching nut. Their purpose is to connect aligned unthreaded holes by being placed through the aligned holes and secured with the bolt’s nut.

 

Bolt Shaft

The shaft is a cylindrical member that bears the shear forces acting on the bolt and prevents the radial movement of the parts. The bolt shaft has two portions:

• The shank (or body) is the unthreaded portion of a bolt located under the head. Its length is measured from the head to the start of the transition to the threads. When installed in a bolt hole, the shank offers precise and smooth contact. Stress is more distributed in this portion than in the threaded portion. Hence, it is necessary to extend the shank until it exceeds the interface of the fastened materials.

The fastened parts may produce or be exposed to vibration, which increases the chance of the bolt loosening. If a bolt has no shank (i.e., the bolt shaft entirely consists of threading), the vibration may push back out of the fastened parts.

• The thread is the continuous helical ridge made on the outside of the bolt shaft. This portion accommodates the nut and allows the bolt to be pushed in or out of the parts. The bolt thread mates with the internal threads of the nut to create a bolted joint. All bolts must have a threaded portion, but most bolts have partially threaded shafts.

 

Bolt Head

The bolt head is responsible for bearing the axial forces that hold the fastened materials. A wrench or a driver grips and applies sufficient torque on the bolt head to tighten or loosen the bolt. Bolt heads come in a variety of profiles and types; some of them are:

• Hex bolt heads have a six-sided, hexagonal head that can be easily gripped by various tools (e.g., wrenches).

 

• Countersunk bolt heads have a conical profile with a flat top. They commonly have a recessed slot to allow screwdrivers or hex socket tools to apply torque and drive the bolt axially.

 

• Dome bolt heads have a smooth and rounded profile. However, they are difficult to wrench externally.

 

Bolts are typically used with the following mechanical devices:

Nuts as Bolt Components

The nut is the female member of a bolted joint that contains a threaded hole. It provides clamping force and prevents axial movement in order to hold multiple parts together. A combination of two forces secures the parts. The nut exerts the axial force, which compresses the fastened parts. This axial force results in a frictional force between the bolt and nut threads, preventing the bolt and nut from being unscrewed. Mechanical locking devices (e.g., lock washers, jam nuts, and split pins) and thread-locking fluids are used if the parts are exposed to prolonged and continuous vibration and impact.

 

Washers as Bolt Components

A washer is a flat, thin plate with a concentric hole at its center. It is typically placed under the bolt head and the nut. Its primary function is to distribute the load of the threaded fastener over a larger area. Thus, the deformation of fastened materials is prevented. Washers made with softer materials such as plastic, rubber, and urethane can effectively dampen vibration, thus preventing the threads from loosening. Special types of washers can prevent liquids from penetrating the bolt joint, creating a waterproof seal.

 

Chapter 2: Fastener Terminologies Related to Bolts

The following are the fastener terminologies used when talking about bolts:

Shank Diameter

The shank diameter is the diameter of the smooth or unthreaded portion of the bolt shaft. It is often referred to as the nominal diameter or body diameter.

Major Diameter

The major diameter is the largest diameter of the bolt thread. It is the distance between two opposite crests or the topmost surface of the thread. The major diameter is often equal to the nominal diameter.

Minor Diameter

The minor diameter (or root diameter) is the smallest distance of the bolt thread. It is the distance between two opposite roots or the bottommost surface of the thread.

Pitch Diameter

The pitch diameter is the diameter halfway between the major and minor diameters.

Basic Dimensions of a Bolt Thread

 

Nominal Length

The nominal length is the total axial length of the bolt shaft, which is equal to the sum of the grip and thread lengths. The grip length is the length of the unthreaded portion, while the thread length is the length of the threaded portion measured from the first complete thread next to the shank to the end of the bolt shaft.

 

Thread Pitch

The thread pitch is the axial distance between two adjacent crests. This specification is used in metric fasteners and is normally expressed in millimeters.

Metric fasteners are manufactured in accordance with the ISO and DIN standards. How do you read metric bolt sizing?

If you encounter a bolt with M10-1.0 x 2.0 sizing:

• M designates that the bolt specifications are in the metric system
• 10 is the nominal diameter in mm
• 1.0 is the thread pitch in mm. Since the thread pitch is specified, this bolt has a fine thread.
• 20 is the bolt length in mm

You may also encounter a bolt specification like M12-50. The thread pitch is not specified in this specification, which means the bolt has a coarse thread. The nominal diameter in this example is 12 mm, while the bolt length is 50 mm.

Threads Per Inch (TPI)

The TPI is the number of threads per bolt thread inch. This specification is only used in imperial or US fasteners. How do you read imperial bolt sizing?

If you encounter a bolt with ¼”-20 x 2” sizing:

• ¼” means that the bolt is ¼ inch in diameter
• 20 means that the bolt has 20 TPI
• 2” means that the bolt is 2 inches long

 

Right-Handed and Left-Handed Threads

Right-handed threads are tightened when rotated in a clockwise direction. It is the most common thread configuration. Meanwhile, left-handed threads advance axially when turned in a counterclockwise direction. These threads are used when the application of pressure causes a right-handed thread to become loose. Left-handed threads are used in bicycle pedals, vehicle wheels, circular saw blades, and gas supply valves.

 

Chamfer and Chamfer Angle

A chamfer is a slightly beveled edge near the bolt tip. It is created by cutting a portion of the first thread near the bolt tip. Some bolts have a chamfered end in order to insert a nut and fit into holes easily. The chamfer angle is measured from the normal to the bolt axis.