[Materials]Aluminum. KINDLY REMINDER that this Aluminum backer-disc is no coating, it can't be used to grinding stone/knife/gem/wood and all other items directly. [Application]This Master Base pad is suitable for the Grinding Polishing Machine. [Function]This Aluminum Master Base Plate is designed as a machine accessory, it's act as a backer-disc sit into the Grinding Machine and the top face for place grinding papers/discs/pads. [Advantage]This Aluminum is Premium workmanship, accurate dimension, well made and plating, soften the edges avoid hurt hand and for comfortable hold. [Applicability] coated flat lap disk grinding wheel can be installed on the aluminum . So if you want to sharpening the gemstone or steel knives, you need purchase a disk( Not included, need to purchase separately), and a aluminum ., Manufacturer: Akfldms