Thin, hollow, sharp-tipped tube used to inject substances into or extract fluids from the body. They are typically made of stainless steel or Niobium, typically individually packaged, sterile, with the tip covered with a plastic cap.
Illustration of a hypodermic needle with the cap on.
They are intended to be disposable and single-use. They are manufactured in a range of lengths and gauges (diameter of the shaft of the needle).
On the opposite end of the shaft, from the tip, is typically a plastic or aluminum hub. The hub is where the scientific or medical apparatus is attached to the needle. The physical connector used to connect said apparatus to the needle is referred to by it’s trademark Luer-Lok.
Gauge (Diameter)
Hypodermic needle gauges are standardized using the Birmingham Wire Gauge standard. The standard specifies the outer diameter of the needle shaft. While the gauge does not specify the wall thickness and subsequently the inner diameter, these parameters are relatively standardized within the medical industry as well, although variants can be found.
The smaller the gauge number the larger the outer diameter. For example, an 18G needle is much larger than a 25G needle.
Standards exist for hypodermic needles ranging from 7G to 34G, commonly available sizes range from 16G to 30G. Anything bigger than 16G and smaller than 30G in my experience can be difficult to find for purchase outside of medical channels.
Lengths
Common lengths for hypodermic needles range from 3/8” (9mm) to 1.5” (40mm).
For typically needle play 1” or 1.5” needles
Longer hypodermic needles are manufactured but these are designed for specific medical purposes and are harder to locate and are typically more expensive to acquire.
Parts of a hypodermic needle.
Additionally, ISO 6009:2016 defines the international medical standard for color-coding of hypodermic needle hubs. Not all hypodermic needle manufacturers follow the ISO standard, so it’s important to read the packaging and pay attention to what you are purchasing and what you are using, but knowledge of the standard is helpful, especially where the it overlaps (e.g. 34G and 25G, 20G and 20G, 33G and 22G, etc.)
Piercing needles are needles used by body piercing professionals to install body jewelry. These needles can also we used for play piercing. There are a few things that differentiate them from hypodermic needles you should be aware of.