What's Needle Cartridge? The needle cartridge uses 12 micro-sized 33 gauge micro-needles to stimulate the dermis faster than a manual dermal roller, resulting in shorter treatment times. With an adjustable needle (depth/length), the Derma pen needles vertically pierce the skin to enhance rejuvenation results, maintain epidermal integrity and reduce patient down time. The penetration depth of the needles can be adjusted directly on the device, so there is no need to change the tip in order to treat areas that require deeper or more superficial treatments. The area of the tip which comes in direct contact with the skin is about 1 centimeter in diameter, which makes it easy to treat hard to reach areas inaccessible to dermal rollers. You can adjust the length of needles and the vibrating frequency, according to your need (0.25mm, 0.5mm, 1.0mm, 1.5mm, and 2.0mm)