What do the numbers cast into the top of some Yamaha bolts refer to? Can't be bolt width, as I have a M6 bolt with 8 cast into the top.

Thanks.

It is the tensile strength of the steel the high tensile bolt is made of. Graded 8.8, 10.9, 12.9.  JIS screws are often just marked up as 7, 8, 10.  The idea is that the maintainer never fits an inferior grade bolt in an application and also knows what the ballpark torque setting should be.  For instance a standard 8mm x 1.25 thread pitch bolt marked 8.8 should be somewhere in the region of 22 to 24nm.  This of course depends on the material it is screwed into also, which is why it is always best to RTFM.

If not marked, it usually means the bolt is not classed as high tensile.

Imperial high tensile bolts are also graded and marked accordingly. Some have three lines radiating out from the centre, some have five and some have six.

 

Thanks both.

I'm surprised that I've not seen the rear sprocket retaining bolts marked accordingly - not high tensile?

Shear vs. tensile strength.

Sprockets have screws that are shouldered in shear and tensile.
Threads are pure tensile(ideally)

No way to grade them due to function and stress direction.

cliff

Thanks Cliff.

I've not come across many shouldered sprocket bolts - see link for RD items.

BOLT BASED HEAD 146254110000 for RD250 1974 USA - order at CMSNL

I'm curious if the bolts marked "8" were Yamaha?  Or perhaps replacements?  I remember Suzuki or Kawasaki and replacement bolts having a stylized number cast on top of the head...  raised, not stamped.  May just be my memory but don't remember seeing numbers much at all on a Yamaha of this era? 

Thanks Mark.

Yamaha definitely had a handful with the casting - see link to a genuine new handlebar mount bolt.

BOLT, HEXAGON (682) for CT1C 1971 USA - order at CMSNL

I remember the Suzuki ones with the "S" casting - I think I read that these denoted high tensile ones.

Anything Honda i've had, [even my car], had #10 tensile strength on bolt heads & you could feel the quality on tightening as just tightened up good & solid.
No stretching & could do them up damn tight too.
Often [if not always] they were wasted bolts with the stem slightly smaller than the thread.
I guess they roll the thread rather than cut it.
Nuts always looked quality too.
Does tensile strength come into play with nuts--& studs. Maybe that's answered up top. I'll go catch up.

Hi Alan,

I would consider that a "replacement" bolt...     

As you know probably better than most of us, many new parts from Yamaha might be "functionally" equivalent...  but not necessarily "cosmetically" equivalent. 

I found several photos of CT1-C's (and other CT models) and all appeared to have unmarked bolt heads on the handlebar mount..

I am very likely 1000% wrong...  I just don't remember seeing those bolt markings very often, it at all, on original Yamaha Enduros?  Especially the earlier models.