Jacobs High Precision Model Taper Mounted Chuck Jacobs high precision model taper mounted chucks are precision tested and certified to 0.0016” T.I.R max at half capacity. Jacobs high precision model taper mounted chucks have a self-tightening feature automatically increases gripping force. Jacobs high precision model taper mounted chucks are proportional to increased torque to prevent tool shank slippage. All Jacobs high precision model taper mounted chuck components exposed to wear are completely hardened to maintain accuracy and extend chuck life. Jacobs taper mount permits use on a wide range of high. Accuracy drill presses, jig borers, milling machines and production drilling equipment.