Hypodermic needles, and the associated syringes, are normally disposable because re-using them or sharing them and their needles can be a means of transmission of many blood-borne diseases.
Normally made of stainless steel, the end of the needle is bevelled to create a pointed (sharp) tip, which allows it to penetrate the skin easily. When a hypodermic needle is inserted, the bevel should be facing upwards.
The size of a needle is commonly stated as a gauge, which is the outside diameter of the needle. Using the Stubs needle gauge, these range from about 7 (the largest) to 33 (the smallest). Twenty-one gauge needles are most commonly used for taking blood. The length of the needle is also stated on the packaging.
There are a number of systems for the gauging for needles, including the Stubs Needle Gauge, and the French Catheter Scale.