Abstract: A fastener and fastener driver system for prosthetic devices and other more common type usages. The fastener is threaded with a driver engaging socket formed in the fastener head. The driver imparts rotational torque to the fastener and includes a drive bit portion engagable with the driver engaging socket formed in the fastener. The driver engaging socket and drive bit are formed with cooperative hexalobular surfaces the sides of which are generally parallel for releasably retaining the fastener on the driver. Each convex curved surface of the hexalobular surface formed on the end of the driver bit is downwardly inwardly beveled. Three alternating concave curved surfaces in the socket are formed with cooperatively mating beveled surface portions. When the driver is engaged with a fastener the beveled surface portions of the socket are triangularly engaged by the driver to securely releasably retain the fastener on the driver to prevent wobbling of the fastener when driven by the driver.