Dr Pen A11 Cartridge Needles 12-pin, 16-pin, 24-pin, 36-pin, 42-pin, and Nano needlesDr. Pen A11 Cartridge Needles are available in the following sizes: 12 pin, 16 pin, 24 pin, 36 pin, 42 pin, and Nano needles each designed to target specific skin concerns and treatment goals. These high quality replacement cartridges are exclusively compatible with the Dr. Pen A11 microneedling pen. Whether you're aiming to reduce fine lines, smooth out acne scars, improve skin texture, or boost serum absorption, there's a cartridge for every skin