Best is stainless steel or ceramic for burr grinder
AVNICUD Manual Coffee Grinder, Ceramic Burr Coffee Grinder with Adjustable Setting, Portable Brushed Stainless Steel Coffee Bean Grinder for Travel,Hand Crank Conical Burr Mill for Precision BrewingManual Coffee Grinder by Cabin Rose - Stainless Steel Portable Hand Grind Ceramic Conical Burr Mill - Maker for Pour Over ...