Screw Thread Charts
Standard Thread Styles
| Deep
Thread: Characterized by a reduced diameter shank resulting in a deep
thread profile. A single lead thread, meaning that one revolution advances
the screw one pitch. (Pitch is equal to 1 divided by the number of threads
per inch. For a screw with 10 threads per inch, one revolution will advance
the screw 1/10" into the wood.) The deep thread form provides superior
resistance to pull-out. The example shown here is the standard hardened
steel Square Drive Screw. Typical part number series include FSL, FPL,
etc. |
Deep Thread |
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| Wood Screw Style Thread: A single lead, extra-thick thread that is used primarily on solid brass
or silicon bronze screws to accommodate the limitations of these soft
materials. Unlike the traditional wood screw thread, the shank is of
uniform diameter throughout most of its length. (Many wood screws are
tapered see tapered wood thread
style below.) |
Wood Screw Thread |
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| Double Lead: Two threads
are wrapped around the shank, as illustrated by the blue and red colored
threads. One revolution advances the screw 2 pitch lengths advantageous on long screws or
in situations requiring rapid assembly. Drywall screws typically use this
thread since pull-out strength isn¹t as important as speed. These
screws lack the pull-out resistance of "Deep" threaded screws.
Typically, #8 and #10 screws 4" and longer use this thread because
of the increased strength afforded by the larger shank diameter. |
Double Lead Thread |
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Tapping Style Thread: Also known as "Type A" or "Wood
Tapping," this is basically a sheet metal type thread. It is a single
lead, fine thread design (meaning more threads per inch). Also, the thread
form is basically an "equilateral" triangle, instead of the special "flattened" triangular
thread which is used for "Deep" threads. Generally, the entire
screw shank is threaded, which makes sense for a sheet metal screw, of
course.
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Tapping Thread |
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| Tapered Wood Thread: Unlike modern extruded thread
screws, "Cut
thread" wood screws have a uniform diameter throughout the length
of the shank. That is because the screw threads are cut into the shank
such that they increase in depth toward the point. Hence the illusion of
a tapered screw. Available in Solid Brass and Bronze only. |
Tapered Wood Thread |
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