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Fasteners: Common
Myths, Misconceptions, and Errors.
The technical library index is to the left in sidebar.

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The heads are breaking: We hate this
phone call more than any other call. In every single case over
the past fifty years, it's never been the screw. Ever. Not
once. Screws have recommended installation torques. Each screw
is different, but it's usually around 1000 to 2000 RPM. When you go faster
than that, the head will sometimes break. That is not a fastener failure
-- that is a user installation failure. "But
I've always done it that way," is a common response. For many years
asbestos was used in ceilings because they've "always done it that
way" --
that doesn't mean it was a good idea.
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SELF-DRILLING versus SELF-TAPPING: These
terms are commonly confused. A self-drilling screw has a drill bit style
point. They are often called Tek® screws,
which is a brand name and not to be used to refer to
generic screws. A self-tapping screw has a sharp point normally and is
a type "A" or "AB" tapping
screw -- though there are other variations, such as "B" point which are
blunt. Confusing self-drilling and self-tapping screws is the single
most common terminology error we run into daily.
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Stainless Steel Doesn't
Rust. That's a commonly
believed statement but it's wrong. Almost all alloys of stainless can eventually
rust because they contain traces of carbon. Any metal that has traces of
carbon can rust. 302, 304, 18-8, and 316 stainless do rust but it takes
a long time. 410 stainless rusts as quickly as steel, but since
it's generally surface rust, the integrity of the screw is
not usually compromised.
- Stainless Steel is not magnetic. In stainless
fasteners, 300 series stainless is non-magnetic in its raw
condition. Cold working it (making the parts) can sometimes cause
traces of magnetism in 300 series, depending on various factors, especially
in washers. An increase in magnetism is caused by the heat and
friction of cold forming and does not reduce corrosion resistance. A higher
portion of nickel can increase stability in stainless, thus decreasing work
hardening and any possibilities of magnetism. 400 series stainless
is magnetic because of its high carbon content. This
articleanswers
the question very well.
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316 stainless is stronger
than 304 stainless: That just isn't true. 316 stainless
may be slightly stronger in many applications using
larger diameter bolts, but 316 is not stronger in any statistically
significant way on most standard sized screws. 316 stainless
does, in most applications, exhibit much better anti-corrosive
properties but that's not a strength issue; see our Technical
Library for more on this.
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Trademark Misuse: This happens often.
People ask for a Tek® when they really want a self-drilling screw.
Or they ask for a Tapcon® when they want a Masonry Concrete Screw.
This happens with many brand names (Tampin®, Red Head®, etc)
but it can be dangerous. Sometimes these brands have significant differences.
It may be hard to believe, but sometimes a fastener costs more for a
good reason. When you ask for a particular brand you are implying that
you want anchors that meet specific technical specifications and
have the proper approvals of the brand name products. More importantly
it's illegal to use a trademark to refer to
a generic item. It's no different than asking for a Coke® and
getting a Pepsi® -- any company that provides
you with a brand other than what you ask for is legally required to tell
you they are doing so: otherwise it's a simple bait-and-switch.
Maybe the substitute you get is as good or better, but maybe it's not:
you just don't know. If you want a Tampin® brand machine
screw anchor, insist upon it. If you think you've been hoodwinked,
asked your vendor for proof or contact the owner of the trademark. (A
good sign of trouble is when the invoice and packaging don't match what
you asked for.)
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Sheet Metal Screws / Wood Screws / Drywall Screws
/ Particle Board Screws: Few
people know the difference. Here's a short summary. As with all rules,
there may be exceptions.
- A sheet metal screw is hardened, fully threaded to at least
3 inches, and has a straight shank. They usually have single lead symmetrical
threads, though double lead threads are common in some industries. The
thread pitch is finer than a wood screw. Most people now use sheet metal
screws instead of wood screws -- this is the most common kind of screw
used in wood, despite the misleading name.
- A wood screw is soft, fully threaded when under one inch in length
and threaded approximately 2/3 of
the screw length when over one inch in length, and has a tapered shank.
They always have single-lead coarse symmetrical threads.
- A particle board screw is hard, fully threaded when under one inch
in length and threaded approximately 2/3 of
the screw length when over one inch in length, and
has a tapered shank. They have asymmetrical threads and are often waxed
or have some form of lubricating agent applied.
- A drywall screw is hard, fully threaded when under one inch in length
and threaded approximately 2/3 of
the screw length when over one inch in length, and
has a almost straight shank. The threads rise well up above the shank
of the screw and they all have a bugle or flat head. If doesn't have
a bugle or flat head, it's not a drywall screw no matter what anyone
tells you. It may be used in drywall but that doesn't make it a drywall
screw. Saying something over and over doesn't make it true.
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Coated vs Uncoated Screws: A lot of people
love to say "oh, the grey screws don't work" or some variant thereof
filling in whatever color may be appropriate for their complaint. Generally
the color of a screw cannot affect its performance in a negative way. Sometimes
the color coatings add a bit of lubricity but they don't cause fastener
failure.
- What screws are RoHS compliant? See our news section for
full details, but a quick summary is: 300 series and 400 series stainless are
RoHS compliant if uncoated and unplated (our part numbers ending in S, 3, and
4) because in most alloys of stainless steel, chromium is in the metallic state,
which is not hazardous. The same goes for other alloys (B, R, and A) The chromium
in the oxide layer of passivated stainless steel, is dichromium trioxide, which
is a trivalent compound. The chromium banned by RoHS is hexavalent chromium.
Zinc and HDG parts are generally not RoHS
compliant unless the label indicates "RoHS compliant" or "Trivalent" or "Cr3"
on it (our part numbers ending in Z, Y, G, Q, H, T, or X.) The actual regulation
reads "..if
stainless steel bolts and nuts are used as parts, they are not considered to
meet the requirement of products specified by Article 5 of the enforcement
regulations (ppIII-268). SO, establishments that purchase such parts and handle
them as components of manufactured products do not have to make a notification.
Regarding the MSDS, if bolts and nuts are used as components by an establishment
and they are not processed through fusion or the like (ie welding), they do
not meet the requirements of the products, thus MSDS need not be submitted."
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