An instrument set (1) for connecting vertebral bodies, comprising a screw (10) which has a screw head (12) and a shaft (14) and can be screwed into a pedicle, a head piece (2) which can be connected polyaxially to the screw (10) for coupling to a rod system (100) and which has a sleeve-shaped tulip (20) having a first insertion opening (21) for insertion of the screw head (12) in an insertion direction (E), and a tool (40), is developed according to the invention in that the head piece (2) has a saddle (30) in the interior region (22) of the tulip (20), the saddle (30) has a receiving region (32) for receiving the screw head (12) in a first end region (31a) that faces the first insertion opening (21a) and a coupling region (35) that can be coupled to the tool (40) in a second end region (31b) opposite the receiving region (32), and the saddle can be moved between a released position (23a), which can be reached by inserting the screw head (12), and a locked position (23b), which can be reached by moving the screw head (12) out of the released position (23a) in the direction opposite the insertion direction (E), wherein in the locked position (23b), the screw head (12) held in the receiving region (32) cannot be disengaged from the receiving region (32), and the saddle (30) can be fixed in a released position (23a) that enables the release of the screw head (12) from the receiving region (32) by means of the tool (40), which is coupled to the coupling region (35). (FIG. 8)
