Abstract: A positioning device for transferring a plurality of carriages or the like into desired positions along a guide, and for holding the carriages in said positions, said device having at least one transfer bar extending along the guide and being movable reciprocally within certain end positions and each carriage having a locking mechanism which, in one condition, locks the carriage to the transfer bar for movement therewith and, in another condition, locks the carriage to the guide, wherein said locking mechanism comprises two pistons movable axially in relation to each other and provided with means for engagement with the guide and with the transfer bar respectively, a pressure medium channel leading to a space between said pistons and one of the pistons being provided with spring means so that with no pressure medium applied said one piston is forced into engagement by the spring force while, upon application of pressure between the pistons, said one piston is released and the other piston forced into its enga