This 20 pcs electric polishing kits are for DIY polished engraving, cutting, polishing (wood, plastic polishing purposes). These are all high quality high speed steel tools with 3mm shank. Features: Apply high speed steel, high hardness, wear-resistant & durable. Suit to engrave, polish, slot materials like wood, plastic. High working efficiency, good grinding effect. 20 different tools, include: rotary burrs, grinding head and rotary burr cutting tools etc. Suits most kinds of rotary tools, electric grinder and electric drill. Perfect to use for wood, plastic, other not hard materials. Specifications: Material: High Speed Steel Shank Diameter: 3mm / 0.118in Total Length: 40mm / 1.57in Package Size: 7.5 * 6.5 * 0.5cm / 2.95 * 2.56 * 0.19in Package Weight: 57g / 2.01oz Note: For better function and tool protection, this set is not suitable for engraving hard wood, metal or stone. It is suitable for wood, plastic and materials doesn't have so high hardness. Package List: 20 * High Speed Steel Rotary Burs