bolts: metric standards

Standards for metric bolts are promulgated by the ISO, but adopted by individual nations. 

Dimensions

A table of major diameters and pitches, up to 30 mm in diameter.

Thread classes of fit

Please go here.

Property classes

In metric bolts, strength is described by “property classes.” A property class designation consists of two numbers separated by a decimal point. There are nine commonly encountered: 4.6, 4.8, 5.8, 8.8, 9.8, 10.9 and 12.9. In the United States, property classes 8.8.3 and 10.9.3 also defined; the "3" after the second decimal point indicates the fastener is made of weathering steel.

markings

Hex head bolts M5 and larger must have the property class marked on the head of the bolt, either in raised or depressed lettering. Fasteners smaller than M5, and those with slotted or recessed heads, whatever their diameter, need not be marked.  Radial lines, such those used to mark SAE grades, are never used on metric bolts. 

drawing of bolt heads marked for property class 8.8

 

 

Property
Class
Fastener
Sizes
 Composition   Marking
4.6 M5-M100     4.6
4.8 M1.6-M16     4.8
5.8 M5-M24;
lengths ≤ 150mm
 cold worked   5.8
8.8 M16-M72 Q&T    8.8
A325M
Type 1
M16-M36 A325M
8S
8.8 M16-M36 Q&T 

 

  8.8
A325M
Type 2
  A325M
8S
A325M
Type 3
 M16-M36  weathering steel;
Q&T
  A325M
8S3
9.8  M1.6-M16 Q&T   9.8
9.8  M1.6-M16 Q&T   9.8
10.9  M5-M20 Q&T    10.9
10.9  M5-M100 Q&T    10.9
A490M
Type 1
M12-M36  Q&T    A490M
10S
10.9 M5-M36  Q&T

 

 

 

10.9
A490M
Type 2
M12-M36 A490M
10S
A490M
Type 3
M12-M36 weathering steel;
Q&T
  A490M
10S3
12.9 M1.6-M100 Q&T   12.9

Key: Q&T= quenched and tempered;

 

correspondence with other grading systems

 

Approximately Equivalent Grades
ISO
class
Inch-based systems
4.6 SAE J429 grade 1
ASTM A 307, grade A
6.8 SAE grade 2
5.8 SAE J429, grade 2
6.8 SAE grade 2
8.8 SAE J429,  grade 5
ASTM A 325, types 1 & 2 (M16 and larger)
ASTM A 449
8.8.3 ASTM A325, type 3 (weathering steels)
9.8 9% stronger than
SAE J429, grade 5
ASTM A 449
10.9 SAE J429, grade 8
ASTM A 354, grade BD
10.9.3 ASTM A 490
12.9 ASTM A 574

ASTM International.
Standard Specification for Carbon Steel Externally Threaded Metric Fasteners (Metric), F 568M - 07.

ISO R898

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