Hole diameter: 6mm/6.35mm/8mm, 3 sizes meet different using needs. Also comes with 2 nuts. High-quality materials: The chuck of the engraving and cutting machine is made of carbon steel materials, which has good flexibility and wear resistance . Fine workmanship and stable performance, portable and easy to use. High precision, tight and stable clamping, improve work efficiency. The router clamp is suitable for engraving wood milling, automobiles, molds and mechanical engineering. Is the perfect woodworking tool for engraving machine, wood router.