The device comprises a transfer unit with a block (44) containing wells (48) in which suckers (50) are located. The wells (48) comprise a border (72) made of a sealing and friction material. The peripheral wall (60) of the sucker (50) is flexible enough to permit axial movement of the lip (62) between an expanded position in which the lip (62) projects above the border (72) of the well (48) and a contracted position in which the lip (62) is coplanar with this border. The internal space of the sucker (50) and the internal space (70) of the well (48) around the sucker are both connected to a vacuum source by respective narrow channels (64,68) whose cross sections are approximately the same as each other. The size of the cross sections of the narrow channels (64,68) is such that there is negligible loss of vacuum inside the sucker (50) when a work piece is placed against the lip (62) but not against the border (72) of the well (48).