Abstract: Well pump rods and similar threadedly interconnected rod members are loosened from their couplings by a device which includes two opposed housing members which are hinged together and support impact blow transmitting members thereon. A latch mechanism including an over-center or toggle linkage is operable to secure the housing in a closed position encircling a tubular rod coupling with the spaced apart and opposed impact transmitting members adapted to receive impact blows and transmit same to the coupling to loosen the threaded connections between the coupling and the rods. The housing provides a suitable support for transmitting impact blows to the coupling and for retaining the coupling in the event of catastrophic fracture of the coupling.