Special forged Hi-Carbon Tool Steel, gold surface treated.
The square shape of these extractors gives the tools the 
ability to remove broken bolts, screws and pipes with
minimum deformation of the broken part. The forged construction
imparts an extra degree of toughness, which reduces extractor 
breakage.  To remove the broken threaded part: Drill a hole in the 
end of the broken part (left hand spiral heavy duty drills are
recommended for this drilling operation), insert extractor and turn 
counter clockwise using a wrench on the exposed end of the extractor. 
The broken part should unscrew without damage to the threads.
These forged extractors will not chew up or expand the object being removed.