McFeeley's offers two types of brass screws: cut thread and rolled thread.
I inquired at McFeeley's site using their online form asking for them to
contrast the two types and have not heard back -- I suspect their email
inquiry mechanism is overwrought with spam, or my spam filters
annihilated any response. Consequently, I seek the wisdom of this more
advanced woodworking group on the question:
What are the advantages and disadvantages of cut thread screws and
rolled thread screws?
Comparing #8 x 1" Flat Head Brass Square Drive reveals:
Cut Thread: $12.88/100
Rolled Thread: $8.92/100
Cut Thread has about a quarter of its length as a shank (no threads),
Rolled Thread has less unthreaded shank. In comparing the two diagrams,
the rolled threads seem more pronounced and may have more of a "bite".
Thank you, in advance.
For the manufacturer, the advantage is a rolled thread screw
can be made in two steps with no loss of material. Roll the
thread onto a wire blank between a pair of hardened comb
plates, then forge the head between dies.
The threadrolling operations I've seen use a heading machine to form
the head (bolt, screw, nail) then off to the threadroller to roll
threads ( or rings on nail ). One advantage for the manufacturer is a
larger diameter product with less material. It work hardens the metal
in some cases.
They grip better. Easier to make a pilot hole with not taper. Seems like
most are made that way if you read the info McFeelys gives. From what I can
see, it is roll from a wire, unlike some threaded bolts that jus roll the
shaft to form the thread.
I've never seen a rolled-thread bolt. If it's rolled, then it's a
screw. Bolts _must_ have a plain shank, and must have a plain shank
that's larger in diameter than the screwthread. They're basically dowel
pins for use in shear with a threaded locking mechanism, not axial
clamps (i.e. screws).
(please check your Machinery's Handbook before posting a rebuttal)
They are however much cheaper to make and much easier to work with..
Upset heading and thread rolling can make 3000+ parts per hour with
almost no waste, a screw machine is closer to 350 and produces a lot of
The tapered pilot holes and increased cost keep the market for cut
On Sat, 13 Jan 2007 18:39:03 -0800, "John L. Poole"
FWIW: From the Lee Valley Web site:
"These are all cut brass screws with well-defined threads and strong
necks, unlike rolled brass screws, which tend to have rougher threads
and are invariably weaker. "
Fascinating. You would think McFeeley's might address the conclusion
that rolled screws are invariably weaker, if only to state it to help
the buyer decide. Referencing the page Edwin so kindly provided a link to:
Given the weakness of brass to begin with, I'd certainly want to know if
two kinds of brass screws vary in strength. Of course, we're not
comparing apples and oranges here since McFeeley's offers cut threads
that are slotted and square drive that are rolled. Maybe a square drive
rolled thread is less likely to fail than a slotted cut thread??
The US Forest Products Lab seems not to have weighed in on this yet with
published experimental data either.
http://www.fpl.fs.fed.us/documnts/fplgtr/fplgtr113/ch07.pdf contains data
and analysis from the pre-rolled thread era. An FPL tech pubs search on
'rolled threads' yielded only one reference and that pertaining to
These folks put forth some recommendations (see page 8)
http://www.pdhonline.org/courses/s168/s168content.pdf however I haven't seen
the research on which it was based so can't comment on its veracity.
Some theoretical observations for the technically inclined:
One must distinguish between the strength (or weakness) of the fastener and
that of the fastened joint. In wood joints, failure most often occurs in
the wood, not in the fastener itself.
For joints loaded in shear rather than tension (fastener withdrawal) then,
for a given nominal screw size, the rolled-thread screw has a smaller shank
(unthreaded portion of screw) diameter compared to a cut-thread screw.
Thus, if the shear joint interface falls at the shank then the lateral
bearing surface will be lower and the bearing stress tending to compress the
wood fibers will be greater.
Conversely, the root diameter of a cut-thread screw is smaller than its
shank. If the shear joint interface falls at the threaded portion of the
screw then the lateral bearing surface will be lower and the bearing stress
on the wood fibers will be greater than if the fastener length had been
selected to cause the joint to fall at the unthreaded shank.
For joints oriented such that the screws are loaded in tension, I believe
that, unless the threaded engagement is extraordinarily long, the failure
mode will be stripping of the threads in the wood (or pull-thru of the
head). That being the case the relative sizes of shank and thread root
diameter will not matter except as the latter determines the height of the
These are much simplified considerations. Also involved would be wood
species, moisture content, grain orientation of both pieces of wood making
up the joint. Beyond that overall joint geometry, point of application and
orientation of the load, geometry of the fastener pattern, significant
deformations of the fastener or joined pieces as failure approaches,
corrosion effects over time, etc. One thing that was mentioned that I can
see no likelihood of being involved in the failure of a screwed wood joint
is 'fatigue'. That is a term applied by metallurgists and structural
analysts to a progressive cracking mode of metal failure due to cyclically
applied loads combined with microstructure and/or electrochemical
Persons screwing together wood joints that are not structurally critical
(i.e., failure could cause harm) can happily ignore such complexities and go
on enjoying their hobby, following only common sense and rules-of-thumb such
as selecting appropriate types of screw and avoiding the use of screws into
end grain whenever possible. However home builders, boat builders and
similar craftsmen of srength-critial structures need to follow established
codes, standards and specifications and seek competent engineering guidance
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