Coupling heads are used to connect the brake circuits in the tractor vehicle to the brake circuits in the towed vehicle.
Tractor coupling heads include an integrated valve which automatically interrupts the power when the lines are uncoupled. Thus the tow heads open the valve as soon as they are coupled to the tractor heads. DIN ISO 1728 heads are the most commonly used heads in Europe, with the exception of the UK, where type C & CA are generally the most common.