A method for mounting a polyaxial screw into a bone includes rotating a drive cap so that a screw mounted to the drive cap is screwed into a bone, the drive cap having a socket in which a portion of the screw is pivotably disposed, at least a portion of a collet being disposed within the socket between the screw and the drive cap. A stabilizing structure and a fastener are positioned onto a shaft projecting from the drive cap. The fastener is advanced along the shaft so as to push a portion of a compression cap against the collet which in turn wedges the collet within the socket of the drive cap and causes the collet to bias against a portion of the screw, thereby locking the position of the screw, the collet, and the drive cap relative to each other.