"Bob" wrote in message
ups.com...
Hi Everyone:

How much pull can a 316 SS PH Machine Screw ¼ x 20 handle before it
fails?

Basically I want to know how many fasters I need to use to secure some
deck hardware.

After an afternoon searching the web I found lots of tech sites with
the info but my math skills are limited to + - x / and don't know how
to convert engineering units to simple old fashioned pounds of pull.

So how many pounds pull can a ¼" x 20 x 2" 316 SS PHMS take before
the nut rips off or the head pops off?

Also, any good rigging/engineering sources for a non engineering type?

Thanks,

Bob

Bob,

The reason you're having trouble finding your "one number" is that it's not
really as simple as that. There's shear strength (failure due to lateral
forces) and tensile strength (failure due to pulling forces) all of which
have different types - yield strength (the force that it can take without
permanent deformation), ultimate strength (the maximum it can stand) and
breaking strength (how much stress it experienced at the point of rupture).
You'd likely want to give yourself a factor of 3 or 4 as a safety margin for
work hardening and galling through overtorquing (with all-stainless
fasteners, too tight is nearly as bad as too loose.)

Typically various fastener strengths are stated in megapascals (MPa) which
you can convert to PSI by multiplying by 145.

I don't know what deck fitting you're looking to secure but I'd suspect that
any failure would occur elsewhere than the screws - heads or nuts pulling
through the deck.
--
Mike Harris
Austin, TX

Mike Harris wrote:

Bob,

The reason you're having trouble finding your "one number" is that it's not
really as simple as that.

There's:

shear strength (failure due to lateral
forces) and

tensile strength (failure due to pulling forces) all of which
have different types -

yield strength (the force that it can take without
permanent deformation),

ultimate strength (the maximum it can stand) and

breaking strength (how much stress it experienced at the point of rupture).

I guess its like asking how big is your boat? GRT, LWL, LOA, LBP, LOD,
pounds, etc

You'd likely want to give yourself a factor of 3 or 4 as a safety margin for
work hardening and galling through overtorquing (with all-stainless
fasteners, too tight is nearly as bad as too loose.)

Yes,
I found a site that mentioned 78 ft lbs is best touque for a 1/4" MS.
Im able to understand that but........

Typically various fastener strengths are stated in megapascals (MPa) which
you can convert to PSI by multiplying by 145.

Yreka or was that Eureka....... Mpa was way over my head. There were a
few othes but I can certainly multiply MPa by 145.

What I would really like to know is how much pullig force can a 1/4 MS
handle befor failing?
But I a not sure how psi would give me a simple pounds of pull? Any
suggestion for converting psi to a simple pounds pulling on the
fastener?

I don't know what deck fitting you're looking to secure but I'd suspect that
any failure would occur elsewhere than the screws - heads or nuts pulling
through the deck.

Yes. Agreed on most cored GRP decks. I am going the epoxy potting and
backing plate routeen. Should increase holding ability significantly.

Thanks for the reply Mike. Sugestoins about that simple number in
pounds or Kg?

Bob

--
Mike Harris
Austin, TX