SCREWS: A USER’S GUIDE
The traditional slotted drive is
still available, but the modern
preference is for cross recessed
or multi-splined (star) drives
to suit modern insertion
equipment. Self-drilling
and self-tapping screws are
available in plated steel and
stainless steel for engineering,
construction and general
assembly purposes.
Specialist Construction
screws are often thought of as
a separate genre but principally
operate in the same way as
their more standard cousins
and tend to be designed
to perform more specific
functions. These functions
range from having integrated
sealing washers, for the fixing
of cladding, through to Bugle
head designs for use in fixing
plasterboard. There are a
variety of drives available,
often linked to the intended
function of the fixing, and
can include designs such as
Hex, Star, Pozi, Phillips and
even Square. Some fixings are
available in a Collated format
where speed and handling is
important.
Largely because of their
wide utility this group of selfdrilling/
self-tapping screws
offer an extensive range of
different head and drive
types. Head types include
the following and may often
be specified with a drive
configuration of choice:
• Pan head: which has a thick
rounded, outer top with a
large surface area
• Button or dome head: which
is cylindrical head with a
dome shaped top
• Countersunk or flat head:
An inverted cone head with
a flat outer surface
• Raised countersunk head:
Combines a countersunk
head with a rounded upper
surface for decorative
purposes
• Bugle head: which presents
a smooth increasing
transition from the shank to
the angle of the head
Thread forming screws for plastics have
become more and more important
in the assembly of everything from
electronic equipment to furniture
• Flanged head: Can be any
head style incorporating an
integrated flange so that it
does not require a washer
Also wafer head – which is
very thin – for use where a
low profile is required.
THREAD-FORMING SCREWS
AND SELF-TAPPERS
Challenge Europe holds in
stock both metal threadforming
screws, e.g. for
castings etc where they secure
components by forming
a machine thread – also
purpose-designed screws for
thread forming in plastics.
The Challenge Europe
team point out that thread
forming tri-lobular screws
are used for fixing into metal
components – a form of selftapping
screw, they use the
tougher tri-lobular design
which assists the grain flow
as it effectively deforms a
thread into thicker material
than could be managed
with a standard self-tapping
screw. This process results
in a thread geometry that is
more accurate than a standard
self-tapper and so provides a
stronger fixing which is more
resistant to loosening under
vibration. Almost a machine
screw in concept these thread
forming screws leave a tapped
hole when removed and may
be replaced with a standard
rolled thread machine screw
if required – for example
at servicing or repair and
thereby provide a much higher
torque loading capacity than a
standard self-tapping thread.
They are typically used in
steel, aluminium, aluminium
die castings, zinc die castings,
magnesium and other light
alloys.
Heads and drives include
countersunk, pan, and
hexagonal/flange types with
cross recess, multi-splined
(star) or hexagonal formats.
Hardened steel is normal
for most applications and is
suitable for use in a variety of
metals providing the correct
diameter pilot holes are in situ.
Stainless steel thread forming
screws are also freely available
but tend to be used in softer
materials such as aluminium
and zinc.
Thread forming screws for
plastics have become more and
more important in the assembly
of everything from electronic
equipment to furniture, as
they are easily inserted into
drilled or moulded holes
in thermoplastic materials
where they deform the
material to provide optimum
fastening force superior to
standard self-tappers. Thread
forming screws are especially
useful in the manufacturing
production environment
where an automatic feed can
be employed to greatly speed
the assembly process, by
eliminating the need for nuts
or inserts, reducing piece part,
labour and process costs.
Challenge Europe
www.challenge-europe.co.uk
01384 262022
26 Issue 2 2020
/www.challenge-europe.co.uk