20 SERVO 12.2015
Types of Screws
Wood screws — as the name
implies — are primarily meant for use
with wood, which itself is rarely the
right material to use in your combat
bot. While there may be only a few
applications for wood in fighting
robots, there are several applications
for wood screws.
When fastening materials like
UHMW-PE and HDPE, wood screws
are a strong option as these materials
(in at least a few critical ways) behave
similarly to wood. The large coarse
threads on the wood screws dig into
the plastic, and are far less prone to
stripping the threads that get cut into
the plastic than most other types of
Machine screws are the all-around
fastener option. You can get these in
a wide range of material, head, and
drive types. For any given thread
size, these won’t be the strongest
option, but they are typically very
budget friendly and can be found
almost anywhere in some form.
Hex head cap screws are the
first step into the realm of
industrial fasteners. At this point,
you’ll often start seeing fasteners
listed as a specific “Grade” or
“Class” when you’re looking at your
options for steel versions of screws.
In general, the higher this
number, the stronger the fastener will
be. For pure strength, these are hard
to beat. However, you’re extremely
limited on head styles, so there will be
many situations where they’re not a
practical option for your build.
Socket Cap Screws
Socket cap screws are another
industrial grade option. Unlike regular
cap screws, there is less choice when
it comes to materials.
However, the materials used for
these types of screws are generally
much stronger than their machine
The other perk of the socket cap
screw over the hex head cap screw is
that you’ve got several head style
options to choose from, which makes
them a much more versatile fastener.
Socket cap screws will more often
than not be the right screw for the
Plastite screws are a specialized
type of screw designed to hold well in
plastic. The shape of the shank is
triangular to resist vibration.
Like wood screws, Plastite screws
have coarse threads that will create
durable threads in plastics.
Flat heads are meant for
applications where you need the
surface of the part being bolted down
to be flat. To use these fasteners
correctly, you need to countersink the
piece of material they’re holding
The countersinking requirement
results in a minimum material
thickness in most cases as the total
head height needs to be contained
within the height of the piece of
material that it is holding in place.
You could countersink into the
material that the screw threads into,
however, this will greatly reduce the
amount of material being held by the
screw and increases the chances of
Hex heads are the highest torque
option since they can typically handle
much higher loads before you’ll risk
stripping the tool-to-bolt interface. The
large exposed head does pose
some risk in combat as they make
for fantastic targets.
However, so long as you keep
that in mind when planning their
locations and you’ve got some
spares handy should any heads be
damaged in a fight, they’re a very
These will typically be the
heaviest screw for a given size and
length due to the bulk of the
head. So, if you’re expecting to be
tight on weight, that may be a
Wood, machine, hex, socket, and Plastite screws.
Flat, hex, socket, and button head screws.