- Basic Types
basic Sems preassembled screw and washer is another
major fastening invention introduced by Shakeproof
that changed industry's assembly methods. All types
of washers - conical, flat, tooth, helical and many
others - can be preassembled to all types of screws.
The many important advantages of screw and washer assemblies
have contributed to their popularity through the years:
small parts handling and dropped parts.
proper parts usage.
purchasing, inventory and assembly costs.
assembly, efficiency and productivity.
conventional flat washer, tooth washer or helical washer
Sems meets the needs of most assembly applications.
Flat Washer Sems span large holes, protect fragile
surfaces and distribute load. External tooth lock washers
are the preferred tooth lock washer style for preassembly
as the tapered twisted teeth are on the largest radius
to provide maximum torsional resistance to removal
rotation. The internal tooth lock washer style is ideal
when the screw head is small - such as a fillister
head - and in applications where it is desirable to
hide the teeth - either for appearance or to avoid
snagging and scratching.
washers are often used on larger diameter screws and
bolts where high torques or heavy loads are involved
and in hardened surface applications where confined
space must be accommodated.
wide variety of other Sems combinations can be provided
for applications involving high torques, load distribution,
electrical grounding, fragile materials, wire termination
or the spanning of larger holes.
and washer assemblies increase torsional resistance
to removal rotation, reducing potential loosening of
the fastener. Sems assemblies not only reduce loosening
caused by vibration but, unlike the locking features
incorporated under some screw heads or on some screw
threads, they also provide a compensating spring action
that resists loosening caused by heat cycling and by
the independent expansion and contraction of different
materials that may make up the assembly.
produced in Shakeproof Assembly Components A2LA approved
facilities assure consistent quality, service and single
can preassemble a wide variety of washers to just about
any type of screw including machine screws, tapping
screws, Tap/R thread rolling screws, GX self-extruding
screws and others. Shakeproof produces Sems in diameters
ranging from a number 2 through 3/8" and in lengths
from 3/16" through 7". All conventional head
styles, drives and points are available.
Here for Terminal SEMS