How to Understand Syringes and Needles

Hypodermic needles with syringes come in many sizes. The right size depends on several factors. Length of the needle depends on type of injection. The most common injections are intramuscular (into a muscle), subcutaneous (under the skin), intravenous (into a vein) or into an IV line. The thickness or gauge of the needle depends on the liquid and amount to be injected. Some substances are thick or large volume and require larger needles. Diabetics use thin needles, as insulin is not thick and injected in small amounts. The syringe size depends on amount of what is being injected.

Instructions

• 1

  Look at the tip of the needle. Below the point is the opening, which is called the bevel. There are different angles and lengths to the bevel, depending on needle length and gauge.

• 2

  Look at the width or diameter of the needle. It is measured in gauges. The larger the gauge size number, the smaller the size of the needle. In the U.S., needles typically use gauge sizes 13 to 31. Diabetics typically use needles that are 27 to 31. A 20 gauge needle is approximately .032 inch or approximately 0.9 mm.

• 3

  Measure the length of the needle from the tip to the base. Needles for subcutaneous or into the skin (intradermal) use may be as short as .25 inch or 6.35 mm. Other needles may be up to 3.5 inches or 90 mm long.

• 4

  Examine the base of the needle. It has a hub that fits into the syringe. In disposable syringes, the connection is solid and cannot be separated. In reusable syringes, you can remove the needle from the syringe and replace it with a new needle.

• 5

  The syringe is the part of the needle that holds the liquid to be injected or holds the fluid drawn out of the body. The tube can be glass or plastic. Inside the syringe is a plunger or piston used to push the injectable material into the body or pull blood or body fluid out. Examine the side of the syringe barrel to determine how much volume it will hold. It is printed with volume amounts. Syringes commonly come in as little as .25 ml up to 450 ml. Diabetic syringes usually are for 1 ml or less and are marked in 1/100 to 5/100 segments.