For nano brows, which is a form of semi-permanent makeup that uses a digital machine to implant pigment into the skin, you should use a specialized nano needle. These needles are typically 0.18mm to 0.25mm in diameter, which is significantly smaller than the needles used for traditional microblading.

The smaller needle size allows for more precise and detailed work, creating a more natural-looking brow. It also minimizes trauma to the skin, which can lead to faster healing times and less discomfort during the procedure.

However, it's important to note that the needle size and type should be chosen based on the individual client's skin type and desired results. A professional technician with proper training should be able to make the best decision.

As a scientist, I would also like to remind you that any procedure involving needles carries a risk of infection, so it's crucial to ensure that the procedure is done in a sterile environment by a trained professional.