The head is the enlarged shape preformed on one
end of a headed fastener to provide a bearing surface
The point of a
fastener is the configuration of the end of the shank of a
headed fastener or of each end of a headless fastener.
ISO : 1478
EN : 21478
DIN : 7970
Core holes for tapping screw and bolts
The essential characteristic of tapping screw
thread is its capability of forming chipless internal thread in
the core hole of the material being joined.
- These core hole data which are theoretically calculated and
based on actual tests are valid for fasteners with tapping screw
thread to DIN 7970 and only for application in metals with
tensile strengths indicated in the tables.
- They cannot be used for plastics. For this application several
modifications of tapping screw thread have been developed.
- They are also not applicable in stainless steel. It is not
possible to provide any general recommendations per case, tests
have to provide the conditions of such joints. The same
situating occurs with stainless steel tapping screws.
- Friction coefficients during screwing-in may be influenced by
coatings requiring adaptation of the core holes. The tightening
torque is primarily dependent on the friction under the head.
- In sheets with thickness up to 2 mm the holes are usually not
drilled but punched. Due to the cold work hardening of the
holewall the holes have to be made 0,1 to 0,3 mm larger,
depending on material and sheet thickness.
Ensure that the screw is torque in the punch direction and not
- Tapping screw thread with cone end type C (previously B) is
mostly used, especially when with more sheets the pilot point
enables the aligning of holes.
- Tapping screw thread with flat end type F (previously BZ) is
preferred for use where the running through, sharp point may
create problems e.g. injuries.