In a well extending from the surface of the earth to a deposit of production fluid there beneath, a system for delivering the contents of the deposit to the earth's surface. The system comprising a rod string capable of being driven by a source of motive power at the earth's surface, including an internally overshot assembly rod at the end of the rod string; a downhole assembly, including a pump and receiver with a shaft extending upwardly from the downhole assembly, the receiver shaft being connectable to the overshot assembly such that rotation of the rod string and overshot assembly drives the pump to push the production fluid to the surface of the earth.