McFeely's 2022 Catalog - Catalog - Page 4
SCREW TECHNICAL DETAILS
Standard Thread Styles
Head Style
Deep Thread: Characterized by a reduced-diameter shank, resulting in a deep thread profile.
A single-lead thread means 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, FRL, etc.
Flat Head: This is the most common screwhead type used for general fastening when the
screwhead will be flush with the surface or when it will be counter sunk and the hole plugged.
Flat heads are generally an 82º taper but may also have a bugle-style taper. Also available in
the widest range of sizes, platings and materials. This type of screw may be used with a trim
washer to convert to a “pan head.” The one screw to have if you can choose only one!
Truss
Head
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 below).
Double Lead: Two threads are wrapped around the shank. One revolution advances the
screw two pitch lengths − advantageous on long screws or in situations requiring rapid
assembly. Drywall screws typically use this thread, since pull out strength isn’t as important
as speed. These screws lack the pull out resistance of deep-thread screws. Typically, #8 and
#10 screws 4” and longer use this thread because of the increased strength afforded by the
larger shank
Pan
Head
Pan Head: Pan heads are dome-shaped and protrude above the surface of the wood. The flat
surface under the head is called the bearing surface and this head style is often used to attach
metal or plastic hardware parts to wood. The higher head profile provides a deep recess that
makes this head style easier to drive. The flat bearing surface also reduces over-penetration
when the head is used directly against wood surfaces.
Truss Head: This head style is very similar to the pan head but has a lower profile and a slightly
larger bearing surface. Since the head profile is lower, the recess is shallower and sometimes
is more difficult for the worker to keep the drive tool engaged in the recess. Some drawer
slides require a lower head height so the screw head will not interfere with the passage or the
slide roller. The lower head is also less obtrusive when seen in the finished product. Most 8-32
machine screws used for attaching drawer knobs and pulls have a truss head design.
Trim Head: The trim head screw resembles a finishing nail in both appearance and function.
The head for a #4 screw is used on either a #6 or #7 screw permitting the screw to countersink
itself, just like a finishing nail. The small head size requires extra care with the driver bit.
Tapping Style Thread: Also known as “Type A” or “Wood Tapping,” this is basically a sheetmetal-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 used for “deep” threads. Generally, the entire screw shank is threaded.
Round Washer Head: A washer is formed as part of the head itself, providing a larger bearing
area that is especially useful when fastening soft materials. They are commonly used when
hanging kitchen and bathroom cabinets and are often used for pocket-hole joinery in exterior
projects.
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 so that they increase in depth toward the point. This gives the illusion
of a tapered screw. Available in solid brass and bronze only.
Super Round Washer Head: Known as drawer front screws because of their common use
in attaching drawer front to box style drawers, Available in three sizes: #8 x 1”, 1-1/8”, and
1-1/4”.
Traditional Wood Screw vs.
Modern Production Screw
The difference between a traditional wood screw and a modern production screws is found in the sizing differences between the diameter of
the screw shank and the screw threads.
Traditional Wood Screws: The shank diameter on this screw exactly matches the outside dimensions of the threads. Threads on these screws
are deeper near the point and begin to shallow as they get closer to the unthreaded shank or screw head. Tapered drill bits are needed with
this type of screw as the pilot hole should fit the outside shank diameter of the screw almost perfectly. Creating this tight fit on traditional
wood screws yields maximum holding power.
Modern Production Screws: The shank diameter is actually smaller than the major diameter but larger than the minor diameter. The overall
reduced shank diameter results in a deep thread profile offering great holding power. Drilling a pilot with a straight drill bit yields excellent
results because the shank of the screw is straight throughout its entire length. The advantages of this are that straight bits
do not require the same critical depth control needed with a tapered bit.
• Minor Diameter: Measurement of the body of the screw between the threads (one side to the other) – Smaller than
major diameter and shank diameter
• Major Diameter: Measurement of the outside of the thread (one side to the other) – Larger than shank diameter and
minor diameter
Size
• Shank Diameter: Measurement of the bare shank (one side to the other) – Larger than minor diameter but smaller than
#10 Traditional
the major diameter
#10 Production
3
Screw Size
Comparison Chart
“B” Body Diameter
Max
Min
“C” Thread Diameter
Max
Mid
0.194
0.183
0.194
0.183
0.157
0.146
0.194
0.183
Pricing is subject to change at any time due to market fluctuations.
