Abstract: A fastening device (10) includes a locking pin (12) and an associated pressing clip (14). The locking pin (12) includes a flat head (16) with ring-like shallow (18) therein for easy operational installation of the fastening device (12) unto the heat sink (100) and the PC board (200). A leg section (20) is provided below the head (16), including four locking legs (22) separated from one another by the slots (24) therebetween and extending downward from the head (16). Each leg (22) defines an enlarged tapered section (26) at the distal end with a shoulder section (28) thereabouts for latchable engagement with the back surface (201) of the PC board (200) around the corresponding hole (202) through which the locking pin (12) extends. A ring-like recess (30) is provided on the middle portions of the legs (22) for lowering the insertion force or preventing unnecessary excessive friction during insertion of the locking pin (12) into the corresponding holes (102, 202) of the heat sink (100) and of the PC board (200).