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Screws
Wood vs. Metal Threading, Dimensions, and
Types of Heads
Screws are basically of two types:
- wood screws are intended for wood and other soft materials.
They have a lower depth on the thread, and
the threads are further apart. Between the
screw head and the threads there is an plain,
unthreaded portion of the shaft called the
shank.
- metal screws have deeper ridges that are closer together
and extend all the way from the tip to the
head . They are intended for use with thin,
strong materials like sheet metal.
Screws come in:
- lengths generally from one-quarter to three inches,
though lags can be much longer. When joining
two pieces, about a third of the screw should
pass through the top piece and the remainder
be anchored in the base.
- sizes of the diameter of the central shaft, called
the gauge, measured at the shank, the smooth
part just underneath the head but before
the threads, from #0 (about one-sixteenth
of an inch) to #20 (about five-sixteenths
of an inch)
The most common types of heads are:
- round head screws are what people commonly think of as a screw,
with semicircular top caps and a flat rim
that fits up against the top material and
may allow it to slide about the anchoring
shank
- flat heads are level across the top and beveled down
to the shank and designed to fit flush with
the surface down into a V-shaped hole countersunk
into the material.
- oval head screws resemble flat heads but that the
top of the screw is rounded slightly to give
the screw a neater, finished look
- pan heads resemble nail heads in order to clasp the
top material
- hex heads tops are shaped like bolt heads
so that hex or socket drivers can turn them
as easily as screwdrivers
Go to the prior page on screws.
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