This is a complicated problem. The common wound treatment of nylon thread 1 # 4 # 7 # takes into account the potential tension caused by skin tension and tissue swelling. Faces can also be stitched with thread 0. The subcutaneous fascia layer can also be sutured with thick nylon wire to reduce skin tension. Generally speaking, triangular needles are used for skin and circular needles are used for skin tissue. Intestinal surgery, especially gastric surgery, uses 1 nylon silk thread in and out, with catgut thread in the middle, which is generally 0/2 ~ 3 in size. If you are not a surgeon, you don't need to go into details. Even if you are a surgeon, the first thing you need to know is the required course. Even interns and interns should let their superiors guide their work and learn from their experience. Practice makes perfect.