Features: brand new and high quality Strong operability: very easy to operate. Versatility: Can be used to clamp drill bits, boring tools, engraving tools, Reamers and other tools have high clamping pressure and high precision. Rugged and durable: Made of excellent manganese steel material, sturdy and durable, and longer using life span. High precision: The tight pressure is large to ensure high precision, Clamping stability: Good blessing stability. Specifications: Material: Manganese Steel Size: A: Six to Three (Optional) B: Six to FOUR (Optional) Product Dimension: Outer Diameter: 6 mm/ 2.36 inches Inside Diameter: 3mm/ 1.18 inches 4mm/ 1.57 inches Total Length: 23 mm/ 9.05 inches Net weight: 100g/ 0.22 lbs Package Includes: 1PC ER Conversion note: Please allow 1-2cm errors due to manual measurement. Due to the difference between different monitors, the picture may not reflect the actual color of the item.