Technical Information · issue 16 of 1999
Screwed Joints in Light Metal Alloys using Self-Threading Screws
IssueTI 16/1999
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Technical Information
16.1999
Screwed Joints in Light Metal Alloys using Self-Threading Screws
1. General Information on DG Screws
Self-threading screws – so-called DG screws (with This lubricant is consumed when a screw is used for
locking teeth on the screw head seating face) – are the first time.
being used to an increasing extent for screwed
joints in light metal alloy components. . No further lubricant is needed when a screw is
installed again in a used component
These screws – like self tapping or self cutting (with formed thread).
screws – require no thread. All they need is a core
hole of the correct diameter.
. On the other hand, if a new component (without
thread) is used, lubricant is required for
When installed for the first time, these screws form
installing the screw (forming the thread). In this
a thread by displacing material – unlike the cutting
case either new (impregnated) screws should
action of thread cutting tapping screws. The material
be used or the existing screws lubricated with
is compressed and this, in turn, strengthens the
oil.
metal and results in a more durable thread.
Important: If “dry” screws are installed in a new
2. Use of DG Screws
component (without thread), the tightening torque
When a “dry” screw is installed in a new component will be reduced. This will result in an insufficiently
for the first time, the friction that occurs while tightened assembly, even if the specified tightening
forming the thread is relatively high. New DG screws torque is used, and may cause the screws to work
are impregnated with a lubricant (“waxed”) to loose or cause a leak (e.g. between engine pan and
minimize the of friction. cylinder).
Note: Screws that are installed in plastic
components (with flat screw head seating face) are
not “waxed” and must not be coated with a lubricant.
© 1999 Andreas STIHL AG & Co. Technical Documentation
Waiblingen D1/MTK 6511
TI_16_1999_30_01.fm
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