A seat comprising: - a seat frame comprising at least a first crosspiece and a second crosspiece positioned at a distance from the other and delimiting a seat space , - a seat made of stretchable material and shaped to at least partially cover the seat space delimited by the crosspieces of the seat frame , the seat comprising at least a first edge and a second opposite edge , the first edge being positioned on the first crosspiece of the seat frame and the second edge being positioned on the second crosspiece of the seat frame , the seat comprising at least one tensioning device comprising: - at least one stiffening member arranged on the first edge , the stiffening member extending at least partially along the first edge , - at least one guide member fixed to the first crosspiece of the seat frame by fixing screws received in bores provided on the first crosspiece , the guide member being elongated and being configured to cooperate with the stiffening member , the guide member comprising a longitudinal housing shaped to at least partially house the stiffening member , the first edge of the seat and at least a portion of the first crosspiece of the seat frame , the housing being arranged in an upper portion of the guide member relative to the direction of mounting of the guide member on the first crosspiece , the guide member being configured to press and block the first edge of the seat and the stiffening member against the first crosspiece , the guide member comprises a plurality of indexing lugs distributed over the length of the guide member , each indexing lug being projecting and extending in a direction substantially perpendicular to the longitudinal direction in which the guide member extends, each indexing lug being configured to be positioned opposite and to be inserted into a respective through hole provided on the first edge of the seat and in a respective bore provided on the first crosspiece . - a seat frame comprising at least a first crosspiece and a second crosspiece positioned at a distance from the other and delimiting a seat space , - a seat made of stretchable material and shaped to at least partially cover the seat space delimited by the crosspieces of the seat frame , the seat comprising at least a first edge and a second opposite edge , the first edge being positioned on the first crosspiece of the seat frame and the second edge being positioned on the second crosspiece of the seat frame , - at least one stiffening member arranged on the first edge , the stiffening member extending at least partially along the first edge , - at least one guide member fixed to the first crosspiece of the seat frame by fixing screws received in bores provided on the first crosspiece , the guide member being elongated and being configured to cooperate with the stiffening member , the guide member comprising a longitudinal housing shaped to at least partially house the stiffening member , the first edge of the seat and at least a portion of the first crosspiece of the seat frame , the housing being arranged in an upper portion of the guide member relative to the direction of mounting of the guide member on the first crosspiece , the guide member being configured to press and block the first edge of the seat and the stiffening member against the first crosspiece , <EOS>