Tattoo cartridges M or Magnum are intended for coloring and shading. Numerical designation before the letter M.
Cartridge Needles M1 or Magnum are grouped into two rows of needles in a loose weaving formation. M2 or Magnum needles are grouped into two rows of needles in a tight weaving form.

What is the basic division of tattoo needles?
What brand of cartridges should I buy?
What do the numbers and letters of cartridges and needles mean?