Metal hypodermic tubing, also called needle tubing, is thin, hollow, round tubing that is used to transfer liquids, air, or solids. It is used in the medical, laboratory, chemical, pharmaceutical, aeronautical and biotechnology industries. Hypodermic tubing is characterized by its small diameter and can be as small as a hair, resembling a fine wire, or as large as a pencil. Because of its round shape with smooth interior walls, hypodermic tubing is pressure-rated, and can provide maximum flow without obstruction. It is measured by gauge, rather than in inches, for its small size.

Hypodermic tubing comes in various construction types including seamless, welded, or welded and drawn. Seamless withstands higher pressure because there is no seam or weld point. Welded construction has a weld or seam; welded and drawn is drawn over mandrel (DOM) to smooth out the inner diameter. When selecting hypodermic tubing, there are several characteristics to consider: outer and inner diameter, material type, and wall thickness.

Diameter is measured in metal hypodermic tubing. Outer diameter (OD) refers to the exterior dimension of a round tube, from outside edge to outside edge. Inner diameter (ID) refers to the interior dimension of a round tube, the width of the area from interior wall to interior wall.

Hypodermic tubing is commonly made with grade 304 stainless steel, also called 18-8, or stainless steel 316 material. These materials are strong, corrosion-, and scale-resistant.

Wall thickness of hypodermic tubing refers to the thickness of the tubing wall. The formula used to calculate wall thickness is OD minus ID, divided by two ([OD-ID]/2). For example, tubing with an OD of 0.5" and an ID of 0.37" would have a wall thickness of 0.065 inches.