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Screws
Screws are metallic, pointed spikes with
ridges (called threads) around the shaft
that bite into material when turned. Because
the threads are really one continuous groove,
pressing and turning the screws clockwise
will cause the screw to penetrate the material,
When long enough to pass through a first
piece of material and into a second, a screw
will hold the two pieces of material more
tightly together than nails and more flexibly
than glue.
Picking the right screw for the
job means
knowing the following about screws:
- types of threading (wood vs. metal threads) and either self-tapping, which mean they
have a point on the end that can bore its
own hole in a material, or regular, which
have no point, and require pre-drilled holes.
- dimensions (length and size)
- types of heads (flat, oval, etc.)
- types of slot - any kind of screw cap may have either
a single slit through the top for flathead
screwdrivers (most common) or a cross for
Phillips head drives (more decorative and
easier to use). Other screws have uncommon
slots to make it more difficult to turn the
screw unless you have the appropriate tool.
These include the star-like indentation in
the head for Torx screw bits, square indents,
and "one-way" screw heads (one
side of the slot is sloped so that the screwdriver
can't grip it.
- composition -screws are made from
- stainless steel for extreme durability
- aluminum to keep from rusting
- brass for furniture or cabinet work
- bronze for lamps and other specialty applications
- ordinary, plated, or galvanized common screws
suitable for any indoor or
outdoor project
where the screws are protected
or not expected
to last more than a few years
against the
weather
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