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Old April 21st 17, 11:16 AM posted to
John B Slocomb
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Posts: 348
Default Selecting An Appropriate Bolt

On Thu, 20 Apr 2017 23:35:32 -0400, wrote:

On Fri, 21 Apr 2017 10:21:56 +0700, John B Slocomb

On Thu, 20 Apr 2017 06:47:57 -0700 (PDT),

On Wednesday, April 19, 2017 at 7:52:25 PM UTC-7, John B Slocomb wrote:
On Wed, 19 Apr 2017 09:12:06 -0700 (PDT),

On Monday, April 17, 2017 at 8:29:53 PM UTC-7, John B Slocomb wrote:
On Mon, 17 Apr 2017 16:19:15 -0700 (PDT), Doug Landau

On Friday, April 14, 2017 at 11:11:18 AM UTC-7, Frank Krygowski wrote:
On 4/14/2017 12:33 PM, jbeattie wrote:
On Friday, April 14, 2017 at 7:27:06 AM UTC-7, AMuzi wrote:
On 4/14/2017 9:14 AM, Art Shapiro wrote:
On 4/14/2017 5:35 AM, AMuzi wrote:

Original handlebar clamp bolts are Grade 8; readily
available and cheap.
Grade 5 may be strong enough but for pennies difference I
suggest an 8.

How does one get these "readily available" Grade 8 guys?
Deda doesn't seem to have much of a web presence outside of
Italy. Is this a generic item stocked by a good LBS?

Any metric fastener supplier if not your local hardware store.

My neighborhood hardware store has them: They have a crazy selection of fasteners.

By the way, what's the deal with thread pitch? I always worry I'm getting the wrong pitch, but I guess that the whole "standard/fine/extra fine" thread pitch only kicks in with fasteners over 8mm(?). Otherwise, it's a pre-set. Right?

No. It's just the charts that only kick in at 8. They are clearly both a)written by someone who doesn't actually know, themselves, and b)plagarising heavily from each other, and repeating the other's mistakes.

There are metric fine pitch threads
like 5mm-0.5 instead of 5mm-0.8

That chart is ****ed up. It says fine but lists more than one thread pitch in the first column, and inconsistently shows extra- and super-fine pitches instead.

The commonly found standard M5 bolt is indeed 0.8 pitch, but the commonly found fine pitch M5 is 0.7. 0.5 must be extra-fine or super-fine. Which is why when you buy a tap and dies set it comes with 5-.8 and 5-.7 but not 5-.5.
I think but am not 100% sure that M6 fine is 0.8 not 0.75.

but I've hardly ever come across them in real life.
No? Are you sure - you've never chased munged up pedal threads? Doing so sends you down to the hardware store for an M10-1.0 tap, because your tap and dies set comes with a 10-1.5 (standard) and 10-1.25 (fine).

There is at least one other place where there is a fine thread, an 8, I think, and I think it's the brake pivot bolt, but am not sure I'm remembering correctly.

What's the thread pitch of derailer hangers?

The "fine thread - course thread" discussion if essentially a very
simplistic categorizing of fasteners. The U.S. Unified thread system
provides a sort of rationalization for a UNC/UNF series but that
didn't and doesn't prevent fasteners being made in a large number of
thread pitches. In U.S. sizes we have, for example, the 1/4"x20tpi
(National Course), the 1/4 x 24 (NS), the 1/4 x 28 (NF), the 1/4 x 32
(NEF) and the 1/4 x 40 (NS).

From memory the difference between American fine and course is the depth of the thread. Course threads cut much deeper into the mating piece to achieve the same amount of metal to metal contact as fine threads.

They are both 60 degree threads but with a flat at the base and peak
and I don't remember whether they are the same. Maybe Frank can check
his Machinery's Handbook (if it is modern enough to include metric
threads :-)

Well, I'm just working from a not very good memory but course threads offer less actual bolt area inside of the threads and hence should not be torqued as high as a fine thread.

On the other hand, fine thread bolts having a shallower thread angle
require less torque to obtain the same clamping force :-)

And it depends what you are threading the bolt into. Using fine
threads in coarse grained cast iron is generally NOT a good idea.

As far as the actual "thread area" there is very little difference. If
you double the TPI the threads are only half as deep, but there are
twice as many threads so the total load bearing area is not much

You missed the point. Because fine threads are at a shallower angle
then coarse threads the clamping (linear) force is greater for the
same torque.

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