A plug for connecting capillaries includes at least one capillary tube, at least one sealing, and at least one pressure piece. The capillary tube includes a first inner diameter and an open end section. The sealing includes a second inner diameter, a first end section and a shape adapted to seal the open end section of the capillary tube when connected. The pressure piece is adapted to exert at least axial pressure and/or force to at least a part of the sealing. The pressure piece is also adapted to host the first end section of the sealing in abutment with the open end section of the capillary tube so that the capillary tube and the sealing are aligned.