Jacobs Chuck professional duty chuck. It has industrial quality. Through hardened jaws provide hard, durable gripping surfaces. One piece sleeve eliminates crack between driving teeth often found in other designs. Fluted sleeve finish. Each chuck 100 percent inspected for performance and precision. It is 1/2-20 mount. 0.063-incehs minimum capacity and 0.5-inches maximum capacity. Measures 1-23/32-inches diameter by 3-inches close length and 2-19/64-inches open length.