Jacobs Chuck ball bearing taper mount chuck. One-piece sleeve eliminates crack between driving teeth often found in other designs. Through-hardened sleeve teeth plus hardened nose and keyholes provide outstanding wear resistance. TIR 0.003-inches maximum at half capacity. 0.04-inches minimum and 0.75-inches maximum capacity. 4JT mount and K4 key number. 5-1/8-inches close and 3-61/64-inches open length. 3-1/64-inches sleeve diameter.