On Fri, 14 Apr 2017 18:15:25 +0700, John B Slocomb
wrote:

On Thu, 13 Apr 2017 20:07:48 -0700, Art Shapiro
wrote:

I had a bit of an adventure when one of the two handlebar-fixing bolts
on my Deda Murex quilled stem decided to snap with a rather impressive
cracking noise. I somehow didn't crash and happened to be only about
seven miles from home. I got slowly home holding the stem with one hand
and one of the brake levers on the dangling handlebars with the other
hand. (This is not recommended to the reader.)

I see that the bolt is a M6x18 tapered cone head Allen cap screw with
pressed-on washer.

The stem is two months shy of 15 years old, but I don't want to have
this happen again. Looking on eBay, I see quite a few appropriate
bolts, but I'm not sure what is optimal. Can anyone help?

Everything seems to be Grade 5. Is that safe enough, or do I really
want to (somehow) find Grade 8?

Many are titanium. Is that a better choice than the more-common steel?
Or should I look for stainless steel? I am always happy to save a few
grams, but not if that's a significant risk.

Advice welcome!

Art

Grade 5 bolts should certainly be strong enough to hold the handle
bars on. But there are grades 8 or 9 that are stronger.

As an aside your description is incorrect. It might be an U.S. size
which might be 8-32 or it might be metric in which case it would be
M8-1.25 or maybe M8-1.0. A U.S. #8 bolt is about half the thickness
of a 8mm bolt.

Generally speaking stainless is no stronger than mild steel and
Titanium is about the same strength as steel of the same hardness.
stainless, of course doesn't corrode much and titanium is about half
the weight of steel.

Your description of snapping sounds seems more like something that was
under great tension.... like over torqued?

Again an aside. The bolt(s) broke once in 15 years.....
The steel bolt may have been "necked down" by rust. Stainless doesn't
do that - but often "welds" itself to the nut - particularly in high
torque installations.