. Made of premium carbon steel with a straight shank and clamping nut for secure tightening. The extension rod diameter and other components are precision ground to minimize imbalance and enhance safety during cutting operations. Suitable for use in engraving, milling, drilling, grinding, and other machining applications. Installation: The shaft diameter is 0.02mm smaller than the bore. Utilizing the principle of thermal expansion and contraction, heat the bore to 300°C using high-frequency heating to expand the hole, then insert the spindle and secure with the locking set screw. Once cooled, the extension rod will be firmly fixed in place. Specification: Material: Carbon Steel Size: ER20A 8mm Package Includes: 1 Piece Collet Chuck Motor Shaft Extension Rod Holder Note: 1. Please allow slight variations in dimensions due to manual measurement. 2. Slight color differences may occur due to variations in monitor displays.