7-051-338 bison precision ball bearing keyless drill chuck 1/32 – 1/2in jacobs taper #6 nc features: keyless drill chucks are precision devices designed for high accuracy applications on either conventional or cnc machines in drilling, boring, and counterboring operations designed to be tightened and released by hand self-tightening feature available in precision quality, 0.005 t.i.r and in nc quality, 0.0015 t.i.r