If your caravan is fitted with an al-ko type stabiliser, then you will require an additional Al-Ko compatible towball.
The Al-Ko can be recognised by its red handle athough there are various styles:
The additional towball has an extended neck that enables the stabiliser to grip more securely.
The head of the towball should be taken back to bare metal to allow for metal against metal grip and should be used completely grease free at all times.
This is reccommened by al-ko and failiure to do so could invalidate your insurance in the event of an accident