Feature: 1. [EXCELLENT MATERIAL] Made of 40Cr and carbon steel, with carburizing and quenching process, high hardness and wear resistance. 2. [FINE PROCESSING] Integrated molding inside and outside of the tool holder, fine control processing, has high concentricity. 3. [FOR MACHINE TOOL] Inner hole grinding treatment, has good stability, suitable for high accuracy machine tool processing. 4. [STANDARD SIZE] The collet extension rod has standard size, fits ER11 collet, and the clamping range is 1‑7mm. 5. [WITH WRENCH] Straight shank tool holder is used with wrench, has high processing efficiency and strong practicability. Specification: Item Type: Extension Rod Product Material: 40Cr + Carbon Steel Product Model: C8-ER11A-100L Shank Length: Approx. 100mm / 3.9in Hardness: 45-46HRC Head Diameter: Approx. 19mm / 0.75in Clamping Range: Approx. 1-7mm / 0.04-0.28in Adapter Collet: ER11 Thread Type: A Shank Diameter: Approx. 8mm / 0.3in . Package List: 1 x Tool Holder1 x Wrench Note: 1. Incorrect assembly may damage the accuracy of the nut and spring2. Only the matching collet chuck can be used to assemble the nut3. Do not clamp tools that exceed the clamping range