the older Johnston couplers. Bell-and-hook coupler The bell-and-hook coupling system was first introduced in the Cape of Good Hope in 1902, when two CGR Type A 2-6-4T locomotives were acquired as construction engines on the new narrow gauge Avontuur Railway which was being constructed out of Port Elizabeth through the Langkloof. In South Africa, these couplers were used on only the narrow gauge lines in the Cape of Good Hope. The coupler is similar to the Norwegian coupler. It is a radial coupler with a coupler pocket which is open at the top of the coupling face. Instead of a link and pins, it makes use of a drawhook which, upon coupling, slides over the drawhook pin in the coupler of the next vehicle in the train. To prevent the drawhook of the mating coupler from accidental uncoupling, the coupler bell is equipped with a drawhook guard, commonly known as a bridle, above the coupler pocket. Usual practice was to have a drawhook fitted to only one of the mating couplers and train crews therefore carried spare drawhooks and drawhook pins on the locomotive. While automatic coupling is possible, this rarely happens and manual assistance is required during coupling. Uncoupling is done manually by lifting the drawhook by hand to release it. The coupler could be adapted to be compatible with the Johnston coupler by replacing the drawhook with a U-shaped adapter link, which was attached using the same drawhook pin. Bell-and-hook couplers began to be replaced on the Avontuur Railway upon the introduction of Class 91-000 diesel-electric locomotives on the narrow gauge system in 1973. All new narrow gauge rolling stock acquired for that line from that year were equipped with Willison couplers. Older rolling stock were not converted and an adapter was used to enable coupling between the two types. The drawhook on the bell-and-hook coupler would be replaced with the adapter, which was attached using the same drawhook pin. Automatic couplers There are a number of automatic train couplings, most of which are mutually incompatible. The level of automation varies and can be divided into categories: mechanical coupling of vehicles only, requires manual connection of pneumatic and electrical lines; mechanical coupling of vehicles with automatic connection of pneumatic lines, requires manual connection of electrical lines; mechanical coupling of vehicles with automatic connection of pneumatic and electrical lines (but not data transmission lines); mechanical coupling of vehicles with