Toruqe De Pernos

Hardware . . .
YOU CAN TELL
A LOT ABOUT A BOLT FROM
ITS MARKINGS!

What’s a Bolt?
In terms of mechanical advantage,
a bolt is an inclined plane. With the
added advantage of a lever—like a
wrench—a bolt can generate tremendous pressure.
A bolt does its job by stretching, just
like a spring or rubber band. Here’s
how:
The tension generated by the bolt
when it’s tightened keeps the nuton
and the connection together. The same
thing happens when you screw a machine bolt into matching threads.
This is how it looks when it’s...

Society of Automotive Engineers (SAE) and American
Society for Testing Materials (ASTM) grade marking chart
BOLT & SCREW
SIZE (in)

PROOF LOAD
(psi)*

TENSILE
STRENGTH
(min. psi)

1/ 4 – 11/ 2

33,000
—

60,000
60,000

1/4 – 3/ 4over 3 /4 – 11/2

55,000
33,000

74,000
60,000

Medium carbon steel,
quenched and tempered

1/4 – 1
over 1 – 11/ 2
1/4 – 1
over 1 – 11/ 2
over 1 1/ 2 – 3

85,000
74,000
85,000
74,000
55,000

120,000
105,000
120,000
105,000
90,000

SAE-Grade 5.1

Medium carbon steel,
quenched and tempered
w/assembled lock washer

No. 6 – 3/ 8

85,000

120,000

SAE-Grade 5.2GRADE
MARKING

Low carbon Martensite
steel, quenched and tempered

85,000

120,000

85,000
74,000

120,000
105,000

MATERIAL

SAE-Grade 1
ASTM-A 307
NO MARK

SPECIFICATION

Low carbon steel

SAE-Grade 2

Low carbon steel

SAE-Grade 5
ASTM-A 449

1/4

1/4

–4

–1

1/2

ASTM-A325
Type 1
ASTM-A325
Type 2

There are tough, strong bolts, lightdutybolts and all sorts of bolts in between. Make sure you’re using the right
one for the job at hand.
Next time you find an empty bolt
hole, resist the temptation to fill it with
the first right-size bolt you find.
...wrench-tightened
Despite their simple appearance,
The extra leverage you can get from
bolts are really precision instruments.
Their job is as critical as any other in a wrench isfantastic. By turning and
turning, you can stretch a bolt comthe operation of a piece of equipment.
When you use a substitute, you put pletely out of shape, snap off the head,
your equipment and your buddies in strip threads, crack the nut, destroy
danger. That substitute bolt can snap at washers—not to mention damaging
what the bolt holds together.
any time.
PS 572
56
JUL 00

Low carbonMartensite
steel, quenched and tempered

85,000

120,000

ASTM-A325
Type 3

...hand-tightened

Medium carbon steel,
quenched and tempered

Atmospheric corrosion resisting
steel, quenched and tempered

–1
1 1/8 – 11/2

85,000
74,000

120,000
105,000

ASTM-A 354
Grade BB

Alloy steel, quenched
and tempered

1/ 4 – 21/ 2
23/4 – 4

80,000
75,000

105,000100,000

ASTM-A 354
Grade BC

Alloy steel, quenched
and tempered

1/ 4

– 21/ 2
2 3/ 4 – 4

105,000
95,000

125,000
115,000

SAE-Grade 7

Medium carbon alloy steel,
quenched and tempered, roll
threaded after heat treatment

1/ 4 – 11/ 2

105,000

133,000

Medium carbon alloy steel,
quenched and tempered
Alloy steel, quenched
and tempered

1/ 4 – 11/ 2

120,000150,000

–1

120,000

150,000

– 11/ 2

120,000

150,000 min
170,000 max

SAE-Grade 8
ASTM-A 354
Grade BD
SAE-Grade 8.2

Low carbon Martensite steel,
quenched and tempered

ASTM-A 490

Alloy steel, quenched
and tempered

–1
1 1/8 – 11/2
1/2

–1

1/2

1/4
1/ 2

* Proof Load is the measure of load that can be applied without causing permanent set.

Bolts Torqueto You
To get the best from any bolt, you’ve got to use the right torque. The torque
called out in the TM isn’t somebody’s best guess, it’s the value built into the bolt.
PS 572
57

The right torque depends on what the bolt is made of and how it’s made.
Typical Torque Values
DIAMETER/ TORQUE LB-FT TORQUE LB-FT TORQUE LB-FT
THREADS
NO DASHES
3 DASHES
6 DASHES
PER INCH
(GRADE 2)...