Hex Head Bolt MarkingsThe strength and type of steel used in a bolt is supposed to be indicated bya raised mark on the head of the bolt. The type of mark depends on thestandard to which the bolt was manufactured. Most often, bolts used inmachinery are made to SAE standard J429, and bolts used in structuresare made to various ASTM standards. The tables below give the headmarkings and some of the most commonly-needed information concerningthe bolts. For further information, see the appropriate standard.

SAE Bolt Designations

SAEGrade

No.Size

range

Tensilestrength,

ksi MaterialHead

marking

1

2

1/4 thru 1-1/2

1/4 thru 3/47/8 thru 1-1/2

60

7460

Low or mediumcarbon steel

5 1/4 thru 11-1/8 thru

1-1/2

120105

Medium carbonsteel,

quenched &tempered

5.2 1/4 thru 1 120 Low carbonmartensite steel,

quenched &tempered

7 1/4 thru 1-1/2 133 Medium carbonalloy steel,quenched &

tempered

8 1/4 thru 1-1/2 150 Medium carbonalloy steel,quenched &

tempered

8.2 1/4 thru 1 150 Low carbonmartensite steel,

quenched &tempered

Bolt Markings http://www.unified-eng.com/scitech/bolt/boltmarks.html

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