Exactoscale Screw Couplings come as a Unit rather than as a what might be referred to as a Coupling.
By a Unit we mean two hooks and one set of D links, threaded bar etc. A Unit therefore allows the joining of two vehicles without the need to purchase anything else. This means that it is cheaper for a modeller, as they only have to buy one Unit rather than needing to buy two complete screw couplings in order to obtain the hook for the adjoining vehicle. Obviously if a modeller wishes to have a screw coupling at each end of every vehicle, then that is there choice, but as only one coupling is ever used to actually connect the vehicle to the adjoining one it seems rather an expensive way of doing things. We therefore gice the option of joinging two vehicles in a cheaper way.
To see exactly what is included in the term Unit please view the following drawings: