US Patent 7073797 Tool holder for annular core bit

A tool holder (1) and a shank (8) for quick mounting and dismounting an annular core bit (2) both include cooperating respective guide members (4, 4′) provided at their bit-side ends, flanges (3, 9) arranged coaxially with the guide members (4, 4′) for axially locking same and having, respectively, outer and inner threads, and outer and inner cone surfaces (6, 10) located inwardly of the respective guide members (4, 4′) and axially spaced therefrom. The outer and inner cone surfaces (6, 10) taper toward their respective bit-side ends. The tool holder and the shank have cooperating torque transmitting elements (5, 5′) arranged between the respective inner guide members (4, 4′) and the respective outer cone surfaces (6, 10).