The Breakaway Safety Cable is an important and essential product when you're towing trailers or caravans.  This is the Clevis and Pin type, PVC coated and approximately 1m in length. 

Braked trailers and caravans must be fitted with a Breakaway Safety Cable which applies the trailers brakes and then snaps off should the main coupling fail. 

If you have an unbraked trailer you'll need a secondary coupling in the form of a cable or chain.  This would connect the trailer hitch to the tow bracket.  This should keep the trailer attached to the towing vehicle if the primary coupling breaks down. 

Please check which type of trailer you have before purchasing.