Jacobs 33363 JK 130-1/2 Industrial Grade Keyless Chuck 1.0 to 13.0 Millimeter Capacity with 1/2-Inch 20 Threaded Mount Automatic fitting for efficient, fast change of tools Machine fitting via DINO238 of Jacobs tapers and UNF thread fittings Self-tightening feature for maximum gripping power Wide range capacity Each chuck 100-Percent inspected for performance and precision