Metric bolt head markings 1

[BillV39]

Suzuki, at least as recently as 2009, has provided a table of standard bolt torques in their motorcycle service manuals that refer to markings on the heads of metric bolts. Two values are listed for each bolt size. The first is for conventional (unmarked) or "4" marked bolts and the second for "7" marked bolts. The table includes drawings showing bolts either unmarked or with a large 4 or 7 on the head.

I am aware of ISO strength grade markings like 8.8 or 10.9 but cannot find any information that correlates with the Suzuki markings. Is this a Suzuki or Japanese system or what?

 

[dinjin]

Why not pose the question to Suzuki?

The values look low. Maybe they are
us grade 4 and 7 ?

If it is their standard on their parts,
what is the concern?

 

[TVP]

Bill,

The markings are likely based on a now obsolete Japanese (JIS) designation system. Grades such as 4T, 7T, and 9T indicate the nominal tensile strength in kgf/mm² x 100, which means that in MPa the values are 392, 686, and 883 respectively. Most Japanese OEM's for automobiles, motorcycles, etc., have their own internal standards that reference the requirements for these fasteners. If you Google something like "bolt JIS 4T 7T" you may find some additional background information.