Abstract: A blow molding die includes a housing, and a mandrel with a core integrated therewith, combined to form a vertically extending annular melt passage communicating with a hole formed at its top portion for feeding a plasticized resin melt from an extruder, and terminating at die lips formed at its free bottom end. The mandrel has a pair or grooves symmetrical relative to its axis, formed at its peripheral surface so as to have hanger type profiles in its front developed view, and connecting to each other at lower ends thereof. The feed hole opens to the symmetrical hanger type grooves at top and central points thereof. Each groove has an arced surface and a cross-sectional area decreasing in a direction from the top and central point to the lower end.

Abstract: In a heat shrinkable synthetic resin cover adapted to seal a joint between two pipes or an electric cable, the cover is made of a rectangular sheet shaped cross-linked polymer and a flexible electric heater covered by a cross-linked polymer contained in a heat shrinkable synthetic resin member such that the electric heater crosses at right angles an inherent direction of heat shrink of the member so as not prevent inherent heat shrink thereof.