Editing Railway coupling (section)

==Buffers and chain==<!-- Do not remove this because an unknown number of pages still redirect here -->

{{Main|Buffers and chain coupler}}
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 [[Plateway|tramway]] practice but were made more regular. [[Buffer (rail transport)|Buffer]]s on the frame of the wagon absorbed impact loads, as the train overran a slowing locomotive.

The simple chain could not be tensioned, and this loose coupling allowed a great deal of back and forth movement and bumping between cars, as well as jarring when trains started. While acceptable for mineral cars, this coupling made for an uncomfortable ride in passenger coaches, so the chain was improved by replacing the center link with a screw with a left-hand thread on one side and a right-hand thread on the other. In the center of the screw is the handle housing with a hinged ball handle attached. This [[turnbuckle]] style arrangement allows the vehicles to be pulled together by tightening the screw with the attached handle. Typically, the screw is tightened until there are two threads left next to the handle housing. A support is attached to the [[trunnion]] nut on the coupling link side to rest the handle of the screw to prevent loosening of the screw while the coupling is in use. The official name of this type of coupling is ''screw coupling'' or ''UIC coupling'' according to the [[European Standard|European standard]] EN 15566 ''Draw gear and 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{{efn|A train with continuous brakes on all wagons.}} 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 in Western and Central Europe and in parts of Northern Africa, the Middle East and South Asia.{{sfn|DAC Report|2020|p=7}}
<gallery mode="packed" heights="140px">
File:Consett-tankwagon41 - buffer beam.jpg|Three-link coupling on an antique tank wagon
File:Eisenbahn Schraubenkupplung 1.jpeg|UIC standard screw coupling, shown attached and tightened
</gallery>