The knock-in pin dowel proposed has a cylindrical outer shell with a non-expandable section of shaft (3) adjacent to an expandable section. The expandable section is divided into two longitudinally abutting or overlapping zones (4, 5) each of which is formed by longitudinal slits (7, 8) and, between the slits, expandable segments (10, 11). The slits (7) in the first zone (4) are closed at each end, while the slits (8) in the inner zone (5) at the end of the dowel closest to the interior of the borehole are open.