Jacobs Ball Bearing Taper Mount Chuck Jacobs ball bearing taper mount chucks feature ball bearing construction that maximizes gripping force and drilling accuracy. Jacobs chuck jaws are center-ground for straightness and alignment. One-piece sleeve eliminates crack between driving teeth often found in other designs. Jacobs ball bearing taper mount chucks feature through-hardened sleeve teeth plus hardened nose and keyholes that provide outstanding wear resistance and feature fluted sleeve standard. Each Jacobs chuck is 100% inspected for performance and precision. T.I.R. 0.003” maximum at half capacity.