A6S Cartridges for Dr penDr. Pen Ultima A6S Cartridges Derma Pen Bayonet Replacement Head Microneedling Pen Needles 11 16 36 Nano Needles Advantage: Original Dr. Pen cartridges for Dr Pen Ultima A6S Microneedling Pen 3 Bayonet Slot The connection of cartridge is with 3 locks design. The cartridge is locked the bayonet easily and firmly, the procedure will be more stable and high effeciency. Fine diameter 0. 18 mm is more compatible with skin texture, less pain and less trauma