Monsgeek M1 plate ANSI Layout not fit for the ISO version M1 DIY Kit. FR4For users who want a balanced feeling between sound and flex.ALUMINUMFor a stiffer and higher-pitched sound profile, for those who want to be heardPOMFor the softest, flexiest typing feeling out of the three.Disclaimer: only Polycarbonate and Aluminum plate comes with screw slots. It is up to the user whether to use them. For other plates, the switches are used to properly fix the PCB and plate to reach ultra-flex experiences.