Scalp vein sets, or butterfly needles, are specialized medical devices used for venous blood sampling. They consist of a hypodermic needle with variable sizes (from 18G to 27G), two bilateral flexible wings, a small diameter transparent flexible tube, and a Luer Lock connector, which can be connected to another medical device, such as a syringe, bag, or bottle for infusion or transfusion. It includes a sliding device and safety lock which is slipped on the needle after use, helping to prevent accidental needlestick injuries and the reuse of used needles, which can transmit infectious diseases such as HIV and viral hepatitis. During venous sampling, the wings are held between the thumb and index finger, and the very close grip on the needle facilitates precise placement into the vein. Successful insertion into the vein is evident by the entry of a small amount of blood into the flexible tube on which the wings are mounted.