With wire-line drilling, a barrel of core can be removed from the bottom of the hole without removing the drill rod string assembly.
When the driller wants to remove the core, an overshot is lowered on the end of a wire line. The overshot attaches to the back of the core barrel inner tube and the wire line is pulled back and the inner tube disengages itself from the barrel. For wire-line drilling, the rods are made of fine-tensile steel. This makes them in, so that the core can be as large as possible.