In article , tomcas says...

Why not just cut a J thread.

He could do that. The main stress concentration
will still be at the thread root that lines up
with the vertical surface though.

Most folks will have trouble getting the specific
thread form like that, but it would probably increase
the strength by about a factor of two or so,
*if* it were a rolled thread. Lathe cut threads
are inherently not as strong so one has to keep
the overall assembly in perspective he

Most times very high strength fasteners are used
in engines where rotating mass has to be kept low,
or in aircraft where overall weight is a major
concern.

Basically any time a simple machine is designed such
that the extra strength of a special fastener is
deemed neccessary, one needs to re-evalute the design
and in most cases simply using a larger fastener
or re-designing the connection is the best way to go.

At one time bmw made their flywheels bolt onto the back
of their crankshafts using special M10 bolts. Waisted,
high strenght steel, relieved shanks and all. Special
torque values and all.

Those machines were *still* prone to spitting the flywheels
off the damn cranks. Their decision for the next
subsequent years models was simple: they went to an M12
bolt that was pretty plain jane. And the flywheels stayed
on from that point.

Mostly the folks who *need* high strength fasteners know
how to do the engineering so they can be used properly.
Those who don't are, honestly, better off 'using the next
size up.'

Jim


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