On Monday, April 17, 2017 at 8:29:53 PM UTC-7, John B Slocomb wrote:
On Mon, 17 Apr 2017 17:51:39 -0400, wrote:

On Mon, 17 Apr 2017 13:52:56 -0700 (PDT), Doug Landau
wrote:

On Friday, April 14, 2017 at 4:15:34 AM UTC-7, 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.

What makes you say this? Do you have some #s to back this statement up, or is it just your wild guess? Have you calculated the load on this part when when a rider of a given weight hits a pothole at a given speed, or ??? And more importantly, why skimp here?

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.

Huh?!? What are you on about? It is you who is incorrect not he. He said it was an M6x18. The x is pronounced "by". Put M6x18 in google and click images. You will see M6 bolts in an 18mm length. He chose to identify the bolt by it's diameter and length, just like the rest of the world does most of the time.


You are right. I'll change my reply to read "It might be an U.S. size
which might be 6-32 or it might be metric in which case it would be
M6-1.0. A U.S. #6 bolt is about half the thickness
of a 6mm bolt." Happy now?
Nope. Please return to the subject, and change your reply to answer the OP's question, which was "Everything seems to be Grade 5. Is that safe enough, or do I really want to (somehow) find Grade 8?"

This will require first identifying the most extreme condition that the bolt will experience as long as the rider can hold on and stay upright. The goal is to determine safe enough, and one is not going to be safe after riding at cruising speed into a wall or curb anyway. Hitting a pothole seems reasonable to me, but whatever. Then calculate the tension on the bolt in that situation, and then compare that to specification for grade 8.

But what is the value in stating "Grade 5 should certainly be strong enough to hold the bars on." ? So will a rubber band or some scotch tape, as long as one rides slow on smooth road.

But there are grades 8 or 9 that are stronger
Yes, the OP knows that, and had to to pose the question "Do I need grade 8?" in the first place.

You are describing bolts using diameter and pitch. This is incomplete, as it does not specify the length. Further is is irrelevant since the JIS and ISO standards both specify 1.0 as the standard pitch for 6mm bolts.

Nope. A thread is described by two things diameter and number of
threads per unit. One can easily buy, for example, a 1/4" thread any
where from a quarter of an inch long, or so, to three feet, or more.

We are not talking about a thread.

If you want to talk length then yes.
Again the OP was talking about grade; you faulted him for the way he described the bolt, and I am saying that a)he described it in the same way we all do most of the time, which is not flawed, and b)the quality of this method which you say is a flaw also exists in your claim of what is correct.

The fact is that a bolt has three identifying characteristics, and all must be expressed in order to avoid being incomplete, and at times, insufficient.