SERVO 12.2015 21
consideration. While it may not seem
like much, it does add up.
Socket cap heads are the second
highest torque option of the four
presented here. Of the three head
styles that don’t use the external
shape of the head for fastening, the
socket cap head will have the largest
tool at any given thread size.
This means you can crank down
on the screw harder and preload the
connection more than the button or
flat head allows.
The relatively small head diameter
does mean that with thin materials
there is a higher risk (than the other
head types) of the head being pulled
through the hole under heavy loading.
Button heads are a decent all-around option. The head height is
fairly low and you can tighten them to
a decent degree. However, compared
to socket cap heads, you won’t be
able to apply as much torque to the
screw before you risk stripping out the
head of the screw.
Button heads are a nice option
for thin materials as they provide a lot
of surface contact between the head
of the screw and the material, which
reduces the chances of the head
being pulled through the material.
The Phillips drive is likely the kind
you’ve used the most throughout your
life. For many common applications, it
has become the default drive style.
It’s not a bad option, but the lack
of high strength screws offered with
Phillips heads and their tendency to
cam-out under heavy loading make
them less desirable for combat
Slotted heads don’t have much of
a place in robot combat. They’re
difficult to drive quickly and typically
are only available with relatively weak
materials. With that said, a slotted
head does have one use.
When you have another style
drive head that’s damaged in combat
or stripped out, you can use a rotary
tool to cut a slot in the head to create
an improvised slotted head that will
allow you to get the damaged screw
Once it’s out, throw it away and
put in a fresh screw.
Where you live will determine
what name you know these by, but
what all of these mean is there’s an
indentation in the head with a
hexagonal shape. These heads are
driven in with Allen/hex drivers of
This head style is available across
a wide range of material and head
types, and provides a good amount of
resistance to stripping. In general,
unless you’ve got a good reason to
use a different drive type, this is the
one you’ll want to use.
Square drives are fairly resistant to
stripping, however, they’re primarily
available with wood screws which
limits their usefulness in robot
combat. If you are going with wood
screws, it is worth considering square
or “Robertson” drives over Phillips
Torx drives are similar to hex
drives but are more resistant to cam-out. From a purely mechanical
standpoint, they’re better, but there
are less screw options available with
torx drives. So, when you’re looking
to standardize on a specific head
style, it may not be the best choice.
Phillips, slotted, hex, and torx drivers.