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Philrock (Mechanical) (OP)
10 Jan 06 17:08
Anybody know where to find proof strength and yield strength (in psi) for inch size alloy steel button head and flat head socket cap screws?  I spent a couple of unsuccessful hours searching on the Internet and in reference books, and talking to manufacturers and suppliers.  Found ultimate tensile.  Found proof, yield, and ultimate for regular socket caps.  But could not find proof and yield for button head and flat head.  If consistent with regular socket caps, specs will be higher for 1/2" dia and under than for over 1/2" dia.
diamondjim (Mechanical)
11 Jan 06 1:41
The thread strengths would be the same.
What may limit the actual strength may
be the head design limitations.
Is that your question?  I would hope that
the head design allows the max torque to
be applied without breaking off the head
of the bolts or screws.
patdaly (Mechanical)
11 Jan 06 8:33
Its been a long time since I was in school, but we were educated that button head and flat head screws were not structural, and not to be used in a critical joint.

That could be why you are not finding any data.
alexit (Mechanical)
11 Jan 06 10:40
Not finding inch size, you can look to mdmetric.com or bossard.com for metric button head and flat head values, maybe ratio vs socket head in similar diameter gets you values?

I too hope weak spot is thread size not head shape...we see more flat head now in structural applications (where visible for appearance I think) than earlier times. No rule against these of I know...
triumph406 (Aerospace)
11 Jan 06 17:37
Look for the Unbrako catalog online, it may have what you need
DC
Philrock (Mechanical) (OP)
12 Jan 06 9:32
Thanks for the help.

I realize that the head is the weak link in flat head and button head screws.

Diamondjim - I would have agreed with what you said until I found concrete information to the contrary.  Material ultimate tensile strengths are significantly lower for buttons and flats than for regular heads.  For 1/2" dia and under, it's 180 ksi for regular heads and 145 ksi for buttons and flats.

Maybe yield is not specified for flats and buttons because it's a moot point - the head pops off before the shank or threads ever get to yield - and ultimate is specified just as a formality, or so a bolt can be compared against the spec with a hardness tester.
Helpful Member!(2)  Screwman (Mechanical)
12 Jan 06 9:59
Both button and flat heads are not intended for structural applications and may fail through the recess under tensile load prior to ultimate strength thread strength being reached.  The actual material strength of the parts is 180 ksi for 1/2 inch and smaller and 170 ksi for 1/2 inch and larger.  The fastener tensile strength are downrated to 80% of this (145 ksi for 1/2 and smaller) to account for the head critical nature of these head designs.
Look to ASTM F835 for more detail.

Here is a quote, "Fasteners meeting this specification are intended for shear type applications and have tensile requirements ranging from 122 to 150 ksi."

Dick
diamondjim (Mechanical)
12 Jan 06 10:32
Way to go Screwman.
I wonder if this limitation would
hold up in court if someone
misapplied these screws.
Thanks for the ASTM F835 reference.
Gave you a star!
Screwman (Mechanical)
14 Jan 06 8:53
That would depend on how good both sides lawyers are. Those are never fun to be in the middle of.  

An old time engineer here always said, "you can have a low head or a strong head, but you can't have both; which do you want".

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