Insulin injection needles are available in a variety of sizes depending on the length and thickness of the needle. The thickness of the needle is marked by the letter G and a number, and the larger the number means the thinner the needle. For example, the diameter of the needle of 32G is 0.2mm, while the diameter of the needle of 29G is 0.33mm. There are several specifications such as 29G, 31G, and 32G according to the thickness of the needle. According to the length of the needle, there are several specifications such as 8mm, 6mm, 5mm and 4mm. Insulin needles are unified needles and can be used with various insulin injection pens sold in the market. Insulin injection needles are single-use devices and are not recommended for repeated use. Repeated use of insulin injection needles can aggravate the irritation of the injection site, easily cause needle blockage, skin infection, and contamination of insulin solution.