Improvements in connector headers of implantable medical devices (IMDs) for making electrical and mechanical connections with a connector element of a proximal connector assembly of an electrical medical lead and components thereof are disclosed. A connector block disposed within a header body of the connector header has a threaded bore aligned with a header grommet aperture and a connector block bore aligned with a header connector bore. A penetrable grommet is disposed within the header grommet aperture, and a setscrew is threaded into the threaded bore having a setscrew socket disposed to be engaged by the tool inserted through the penetrable grommet within the header grommet aperture to enable rotation of the setscrew within the threaded bore to tighten the setscrew against or to loosen the setscrew from a lead connector element received in the header connector bore.