Bolt Strength Chart and Grade Marking Chart

What is Bolt Strength Chart?

A bolt strength chart is an important tool for calculating the tension or clamp force that a bolted joint can withstand. It is used to select the correct size and type of bolt for specific applications, ensuring that the joint will be strong enough to handle any load it may incur.

The below bolt strength chart shows the amount of tension each type of bolt can reliably take before fatiguing or breaking under stress.

Commonly used Bolt Grades

The most commonly used bolt grades are:

1. Grade 2,
2. Grade 5,
3. Grade 8,
4. Grade 307A,
5. Grade A325,
6. Grade 651.

US Bolts

Marking on Bolt Head	Grade & Material	Nominal Size (in inches)	Mechanical Properties
			Proof Load (Ksi)	Minimum Yield Strength (Ksi)	Minimum Tensile Strength (Ksi)
	307A Low carbon steel	1/4″ to 4″	N.A.	N.A.	60
without Markings	Grade- 2 Low/ medium carbon steel	1/4″ to 3/4″	55	57	74
		Over 3/4″ to 1.5″	33	36	60
3 visible Radial Lines	Grade 5 Medium carbon steel, quenched & tempered	1/4″ to 1″	85	92	120
		Over 1″ to 1.5″	74	81	105
6 visible Radial Lines	Grade 8 Medium carbon alloy steel, quenched & tempered	1/4″ to 1.5″	120	130	150
	Grade A325 Carbon or alloy steel with or without boron	1/2″ to 1.5″	85	92	120
Markings on stainless steel Vary	18-8 (304) & 316 Stainless Steel alloy with chromium and nickel	All sizes thru 1″	N/A	minimum 20 but 65 Typical	minimum 65 but 100 – 150 Typical
	651 Silicon bronze silicon bronze bolt	1/4″ to 3/4″	N.A.	55	70
		7/8″ to 1.5″	N.A.	40	55
	Aluminum Grade 2024 Aluminum bolt	All sizes	N.A.	36	55
Metric Bolts
Marking on bolt head	Bolt grade & Material	Nominal bolt Size (mm)	Mechanical Properties
			Proof Load (N/mm2)	Minimum Yield Strength (N/mm2)	Minimum Tensile Strength (N/mm2)
	8.8 Class Q &T Medium carbon steel	Almaximum 16 mm	575	650	800
		16 to 72 mm	600	650	830
	10.9 Class Q & T ( quenched & tempered)	5mm – 100mm	830	940	1040
	12.9 Class Q & T ( quenched & tempered) Alloy steel,	1.6 to 100 mm	970	1100	1220
generally marked A-4 or A-2	A-2 & A-4 Stainless stainless steel	sizes up to 20 mm	N/A	minimum 210 450 generally	minium 500 700 generally

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