A turntable is a system making it possible to make make half-turn with the railway materials which have only one direction of control, such as some locomotive with vapor either in the deposits, or in the terminals or to carry out the putting up of the coaches or cars in the first stations.

It is composed of a lining in the center of which a pivot is which supports the plate. A Rail curved makes the turn of this pit and supports the ends of the plate. The turntables used in Narrow gauge railway are often in cast iron of cast steel. Their diameter is of approximately one meter. Their counterparts in normal Voie have very variable dimensions: of 5m approximately for the coaches to 28 m for the plates of large deposits.

In these deposits, the turntable is often surrounded by a Rotonde. Thus, one can arrange a great number of engines in a reduced space, all the machines being accessible easily.

If the turntables for coaches remained well of the turntables those for the machines became revolving bridges by the suppression of the palettage surrounding the central part where are the rails and recovering the lining.

Old the Tramway S required also turntables to be turned.