Mast Sai tattoo pen has an interchangeable stroke length 3.2mm, 3.7mm stroke and has a soft and hard adjust knob. Mast Sai rotary pen tattoo machine has strong power, super stable, Pretty quiet - low noise, it is quite easy to master. Carved by aircraft aluminium alloy enclosure Compatible with all stardard cartridges needles. This machine features a powerful motor and exquisite appearance,Light weight, super stable. This rotary tattoo machine simple, classic, and the most suitable machine for precise line work, black and grey shading, solid color packing. Operating Voltage: 5-10V,The max operating voltage is 10V. Don't run it higher than that or you'll overheat the motor and cause mechanical wear.