Indirectly trike related Q on bolt shaft vs. head size.........no not that

[RUNMEDOWN]

So the charts I have show any metric bolt with a 10mm head should have a 6mm shaft and any bolt with a 8mm head should have a 5mm shaft. But I have bolts that have 8mm heads and 6mm shafts (Case bolts - hold pull start on 185s). Am I going nuts here or is there actually variation that I have not run into in 39 years? (I just snapped off a 10mm headed bolt with 6mm shaft in the case so I have to extract and all the replacement bolts have 8mm heads but are the same length and thread (6mm 1.25) size/pitch)

[wonderboy]

I didn't think there was a standard convention here...

Even on the Honda's, they'll use an 8mm hex and a 10 mm hex for an M6 bolt, depending on where it is. Many of the M6 fasteners I've bought at the hardware store have used an 11 mm hex head.

And the head style on the Honda OEM bolts is unlike any that I've been able to find an exact match for anywhere... except from Honda themselves.

For the case bolts, the smaller head makes sense since you have limited clearances. The smaller 8mm hex allows a smaller socket...

So bottom line, I don't think there is any universal standard for size between the hex and the thread.