Tail piece for an extendable drill bit assembly having a reduced head

An assembly comprising:

• a quick-release head having a wall defining a bore and a ball engaged with said wall and moveable relative thereto;
• a tail piece including a shaft portion, a male coupler portion provided at an end of said shaft portion, said male coupler portion including a head having a proximal end, a distal end and a length defined between said proximal end and said distal end, said head of said tail piece defining an outer dimension, a body having a proximal end and a distal end and a length defined between said proximal end of said body and said distal end of said body, said body defining an outer dimension, and a flute extending between said distal end of said head of said tail piece and said proximal end of said body, the head of said tail piece having a reduced outer dimension relative to said outer dimension of said body, the reduced outer dimension extends 360° around said head of said tail piece and is constant along the entire length of said head of said tail piece;
• and
• a flexible rod connected to said tail piece;
• wherein when said tail piece is seated within said bore of said quick-release head and said ball of said quick-release head is seated within said flute of said tail piece to prevent release of the tail piece from said quick-release head, a clearance space is provided between said head of said tail piece and said wall of said quick-release head along the entire length of said head of said tail piece, such that transfer of drive forces from an associated drill are predominantly shifted to the body.