In the mechanical production field the best way for connecting the tool to the machine tool is a taper: the force is transmitted along the lateral surface in a more or less rigid way. The spindle drawbar pulls the homonym stud to keep in contact the 2 surfaces of the tapers.
The force required is between 15-60 kN, depending on size and norm used.
HSK is around 40 kN for HSK-A 100, the biggest model.

The main difference between the 2 solution is the way they pull the cone: HSK from the internal side, all the others managing the pull stud in the rear part of the cone.

A sort of HSK bible can be found here.

For testing the force, during the construction of the head or the machine in general, it’s possible to use this device: the instrument has the shape of a cone and it’s connected to a mainboard with a digital display. Opening, inserting the tool and reading the value is the simple procedure.


Test instrument

Complete set for testing

There are 6 kinds of HSK:

Type Good for
A Automatic tool change (ATC) – default
B Automatic tool change (ATC) – big torque
C Manual tool change – default
D Manual tool change – big torque
E Low torque, very high speed
F The same as “E” type

The movement of HSK bulb, in advance, creates a fall of the gripper petal that releases the taper. During folding, the bulb, which is united with the gripper, fixes the latter against the taper, and the whole group consequently (see the scheme below).
In yellow the moving contact zone in a HSK gripper.


HSK 100 contact zones
Schema apertura

Gripper opening sketch

Here the main differences betweeen the HSK and the other solutions:

Feature HSK Other
Radial stiffness 5 1
Torsional stiffness 1 1
Accuracy 1 1
Run-out 1.2 1
Transmitted torque 9000 Nm in HSK 100 7500 Nm
Presetting Better, no change in tool tip with wear Worse, chenge in tool tip position after wear
Strain The harder you go, the more torque you transmit The harder you go, the less torque you transmit
Strain at high speed Same tool tip (no change in axial position) Change in tool tip position because of centrifugal forces
In the event of a collision Acts like a fuse The force is transmitted in full
Service cost High. Qualified personnel is required Low
Tool change speed Fast: the cone is light Slow: the cone is heavy
Wear sensitivity High (tighter tolerances), the personnel must be trained Low
Cost High, but the increasing demand is reducing the gap Low
Coolant sensitivity at ω>> High, because of displacement High, because of displacement

In general, we can split grippers in a geographic way:

Tool holder norm Place Notes
DIN 69872 A-B, ISO 7388/2 A-B Europe /
ASME B 5.50 America /
MAS 403 PT1-2, JIS Asia /