page_title: Railway coupling
section_title: Buffers and chain
hierarchical_section_title: Railway coupling / Buffers and chain
caption_attribution_description: Carrage couplings on ABT Railway
context_page_description: A coupling is a mechanism used to connect rolling stock in a train. The design of the coupler is standard, and is almost as important as the track gauge, since flexibility and convenience are maximised if all rolling stock can be coupled together.
  The equipment that connects the couplings to the rolling stock is known as the draft gear or draw gear.
context_section_description: The basic type of coupling on railways following the British tradition is the buffer and chain coupling. A large chain of three links connects hooks on the adjoining wagons. These couplings followed earlier tramway practice but were made more regular. Buffers on the frame of the wagon absorbed impact loads, as the train over-ran a slowing locomotive.
  The simple chain could not be tensioned and this slack coupling allowed a lot of back-and-forth movement and banging between vehicles. While acceptable for mineral wagons, this coupling gave an uncomfortable ride for passenger coaches, and so the chain was improved by replacing the centre link with a turnbuckle that draws the vehicles together, giving the screw coupling. 
  A simplified version of this, quicker to attach and detach, still used three links but with the centre link given a T-shaped slot. This could be turned lengthwise to lengthen it, allowing coupling, then turned vertically to the shorter slot position, holding the wagons more tightly together.
  Higher speeds associated with fully-fitted freight made the screw-tensioned form a necessity.
  The earliest 'dumb buffers' were fixed extensions of the wooden wagon frames, but later spring buffers were introduced. The first of these were stiff cushions of leather-covered horsehair, later steel springs and then hydraulic damping.
  This coupling is still widespread.
caption: Screw-tensioned three-link coupling. The narrow buffers of the left-hand vehicle are sprung, the thicker buffers on the right contain a hydraulic damper.
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