When ball knobs DIN 319 (Press on type) type L and M are used the shaft does not require a thread.
During mounting, easy blows with a soft hammer are sufficient to drive the knob into place, the shaft end should be slightly rounded or chamfered (30°).
Before the assembly of the knobs, type L the tolerance ring is to be inserted into the drilling. Further it is to be noted that the button is put on perpendicular and / or axially parallel. Otherwise the knob may break.
Type M ball knobs are a cheaper solution, however, the pulling off force is less predictable.