DIN 931

Product grades A and B

This International Standard specifies the characteristics of hexagon head bolts with threads from M1,6 up to and including M64, of product grade A for threads M1,6 to M24 and nominal lengths up to and including 10d or 150 mm, whichever is the shorter, and product grade B for threads over M24 or nominal lengths over 10d or 150 mm, whichever is the shorter.

Commercially, the steel quality used to manufacture of the DIN 931 grade 8.8 bolts includes Grades A2 and A4 class 70. The tensile strength for both these steel grades is around 700 Mpa. The strength of the DIN 931 bolt M10x18 is indicated by the marking on the head and it is also defined by the applicable product standard. The A2 version of the DIN 931 bolt material is manufactured from Stainless Steel grade 304, which is known for its Corrosion Resistant properties.

This can be attributed to the high content of chromium and nickel in the alloy of the DIN 931 bolt M8x15 (Metallurgical, the A2 or the ASTM-304 has a designation of 18/8 Stainless Steel or 18% Chromium & 8% Nickel). Although the A2 is mostly considered to be a non-magnetic austenitic stainless steel grade, some residual magnetism of the alloy can be introduced when the material of the DIN 931 Bolts

Similar to the A2, the A4-70 DIN 931 bolt material specification is an austenitic, acid proof stainless grade. Usually, the A4-70 is manufactured from stainless steel grade 316 material or its low carbon variant grade 316L. stainless steel grade 316 has been cold worked to provide a minimum tensile DIN 931 bolt strength of 700 MPa.

As compared to stainless steel grade 304, grade 316 provides better overall corrosion resistant properties. This holds true particularly as grade 316 stainless steel has a higher resistance to both pitting as well as crevice corrosion in chloride environments. The good corrosion properties of the DIN 931 hex bolt manufactured from Grade 316 stainless steel can be attributed to the high molybdenum content in its alloy.

Specifications and reference International Standards
Material Steel Stainless Steel Non-ferrous metal
General Requirement As Specified in Din 267 Part 1
Thread Tolerance Class 6g
Standard DIN 13 Parts 12 and 15
Mechanical properties Property class 5.6, 8.8, 10.9 d ≤ 20 mm: A2-70, A4-70
d ≥ 20 mm: A2-50, A4-50, C3,C4
Subject to agreement
Standard DIN 898-1 DIN 267 Part 11 DIN 267 Part 18
Tolerances Product grade For d≤ 24 mm and l ≤ 10d or 150 mmb: A
For d> 24 mm or l > 10d or 150 mmb: B
Standard ISO 4759-1
Surface integrity As process property class 8.8 and above : (thermally or chemically blackened) Bright Bright
DIN 267 Part 2 shall apply with regard to surface roughness.
DIN 267 Part 19 shall apply with regards to permissible surface discontinuities.
DIN 267 Part 9 shall apply with regards to electroplating.
DIN 267 Part 10 shall apply with regards to HDG.
Acceptability   DIN 267 Part 5 shall apply with regards to acceptance inspection.
a) Other property classes are specified in ISO 898-1 for steel and ISO 3506-1 for stainless steel, respectively.
b) Whichever is the shorter.
Marking of Bolts

Hexagon head bolts according to this document shall be marked with ISO 898-1.
a) Property class marking in accordance with EN ISO 898-1.

Example 1 8.8

b) Identification mark of the RFL.
It is permissible for the marking to be either embossed or indented on the top surface of the head.

Example 2 bolt making


Example - A hexagon head bolt with thread M16, nominal length l = 100 mm and property class 8.8 is designated As follows:
Hexagon head bolt DIN 931 - M16× 100 - 8.8.