An instrument for assembling a bone anchoring device includes a shank with a shaft section to be anchored in a bone and a engagement end, a head being separate from the shank and having a through bore, and a receiving part having a first end, a second end and a longitudinal bore extending from the first to the second end, the head being positionable within the bore at the second end. The instrument includes a holding portion arranged to hold a pin, which has a rod section with a length and a diameter suited to fit and extend at least through the bore of the head, and which has a free end portion extending from the rod section such as to project from the bore of the head when the pin is inserted, and configured to engage with the engagement end of the shank.
