aluminum alloy, this adapter rings is and can withstand high pressure and frequent use, guaranteeing a long Perfect for coffee grinding, avoid spillages, no more mess and spilled over grind Simply twist the funnel onto your 58mm portafilter, aligns the funnel with the grinder, gently press forward to the auto-grinder, and release This espresso dosing funnel helps collect and tamp all of your coffee grounds in your 58mm portafilter with ease, the grounds can be tamped without the dosing funnel Perfect for coffee enthusiasts who seek to control the extraction and taste of their coffee by replacing the tamper base