The UK formerly used three-link couplings, which allowed a large amount of slack; these were soon replaced on passenger stock by buffers and chain couplers where the couplings are held tight by buffers and shortened by a turnbuckle while in most other parts of the world automatic couplings, such as the Janney coupler and the Scharfenberg coupler, were adopted from the late Nineteenth Century on. Three-link couplings are a rarity in modern use.
