In the process of fitting the Polymer into the junk cover, an engineer loosened the screws from the junk cover and secured it with only 1 screw. Once the fitting of the Polymer was complete, he observed one of the crew with his fingers in a pinch point area (between the hanger & junk cover), he decided to intervene and show him the hazard associated with pinch points. While doing so junk cover dropped and struck the engineers left hand little finger.