An instrument for attaching a driver shaft to a screw assembly using a thrusting motion. The instrument has a main shaft, a locking tube, and a driver shaft. The locking tube is slidably mounted within the main shaft and the driver shaft is slidably mounted within the locking tube. The locking tube is configured to urge a jaw assembly of the instrument into a tensioned engagement with a body member of the screw assembly. A locking mechanism is also included and is configured to lock the driver shaft in a fixed position relative to the locking tube. The locking mechanism may be configured to lock the driver shaft with respect to the locking tube after a distal end of the main shaft engages the screw assembly using the single action.