An impact power tool has a drive anvil with a square drive lug at one end thereof provided with a peripheral groove formed therein adjacent to its distal end. A socket tool body has a square socket receptacle mateable with the drive lug and defining flat planar drive surfaces. A bore extends transversely through the socket body and the receptacle substantially tangent to one of the surfaces so as to communicate with the groove when the drive lug is received in the receptacle while being retained in place by a pin receivable through the bore and the groove. Extension and adapter socket tools are disclosed.