Three rapid draws on device to adjust voltage. Two rapid draws for pre-heating: Green(3.0V), Red(3.8V), Rainbow(Preheat) Electroplated - New Stylish Metallic Coating, High Privacy Vaping with great style Fits with most 510 Cartridges (maximum – 11.5mm) USB-C Cable Included Instructions: Three rapid draws on device to adjust voltage. Two rapid draws for pre-heating Voltages: Green – 3.0V Red – 3.8V Rainbow – Preheat