The anatomy of the hypodermic needle and syringe

This article has been written to explain how syringes are constructed, and the terms used to describe the component parts.

Although written for drug workers so they can discuss needle and syringe selection with authority when discussing the issue with injecting drug users it will also be of interest to other health professionals, and injecting drug users.

It answers some key questions:

• what are the names for the parts of a syringe?
  

• what is the difference between a 2 part and a 3 part syringe?
  

• what are the different needle fitting systems?
  

• what is the meaning of 'high dead space syringe' (HDSS) and 'low dead space syringe' (LDSS)?
  

• what do needle length and gauge mean?
  

• what is needle bore?
  

At the bottom of the article, there are links to all these products, which you can buy from us.

Syringe construction
Excluding the needle (which can be attached or separate - more on that below), syringes can be constructed with 2 or 3 parts.

A 3 part syringe has the barrel (the outside of the syringe, which has the graduations and name printed on it), the plunger AND a rubber plunger cap to form a better seal between the barrel and the plunger – most of the syringes we stock are 3 part syringes.

However, 2 part syringes are commonly used in mainland Europe. In a two part syringe, the plunger is engineered to form a perfect fit, and there is therefore no need for a separate synthetic rubber plunger. Three part syringes tend to have a smoother feel, which is why all Exchange Supplies syringes are 3 part syringes.

Attaching the needle to the syringe – 3 methods

There are 3 ways needles are attached to syringes, they can be:

• Twisted onto a Luer lock fitting;
  

• Pushed onto Luer slip fitting; or manufactured as
  

• Fixed needle all-in-one type syringes.
  

These are described below.

Luer lock
Luer lock syringes for detachable needles work by having a twist fit thread around the tip of the syringe for the needle to screw down onto form a more permanent seal. ALL detachable needles have two small tabs on the outside that fit into this thread, so that they can be fitted to luer lock syringes. In 2015 we switched the 2ml Nevershare to a luer lock fitting, because of the extra security this gives the needle.

Luer slip
Of the 'detachable needle'type of syringe, the most commonly used system is the luer slip fitting.

The 'luer slip' is a universally agreed taper that ensures a leak-proof connections between a syringe (the 'male part' of the taper) and a needle (the 'female part').

The fitting is named after a German medical instrument maker called Hermann Wülfing Luer. The exact dimensions of the 6% conical Luer taper connectors are defined by an internationally agreed standard - and adherance to these dimensions mean that needles made by any manufacturer will fit any and all luer slip syringes.

The needle is fixed to the syringe by simply pushing it on, usually with a small twist to increase the purchase and grip as it attaches. The name luer slip understates the quality of the seal that is formed as the needle is firmly fixed to the syringe. Although it is only held on with friction (there is no thread) the seal is so good, luer slip syringes are sometimes erroneously called luer lock syringes.

Fixed needle syringes
Syringes can have the needle fixed during manufacture – this is done with tuberculin syringes and 1ml insulin syringes such as the Omnican, and with our 1ml nevershare syringe developed for injecting drug users.

Fixed insulin type syringes such as the 1ml nevershare have no void space at the point where the needle joins the syringe, and so are known as Low Dead Space Syringes, which is sometimes abbreviated in the literature to LDSS. They are made like this so that the full accurate dose is delivered, and there is no waste.

The significance of this in blood borne virus prevention terms is that distributing LDSS is likely to result in significantly lower levels of HIV and possibly Hepatitis C transmission.

The dead space in the luer slip fitting
In the field of blood borne virus transmission, luer slip syringes are termed 'high dead space syringes' or HDSS.

This is because after injection, the void inside the luer slip fitting is often left filled with blood. The volume of blood in the luer slip is much greater than in insulin type sringes such as the Nevershare (which are termed 'Low Dead Space Syringes' / LDSS).

High Dead Space Syringes can carry significantly more virus particles and so presents a much greater infection risk.

There is some evidence that blood borne virus epidemics spread more slowly in cities and regions where LDSS are predominantly used than in those where injectors have historically used HDSS.

Needle Gauge (the circumference or thickness)
During the industrial revolution, when the manufacture of wire for fencing and other uses was perfected, a system was developed for describing the thickness of the wire.This was called the gauge.

Confusingly, the bigger the number the narrower the gauge.On the labelling and boxes for needles, where the gaugenumber is given, the word gauge is always shortened to just the letter ‘G’. The gauge system is used all the way down, even to things as thin as needles for injecting.

The gauges used for injecting range from 30G (the finest) to 21G (the thickest). The different gauges are allocated a colour, so that people can, at a glance, determine the thickness of the needle. The colour coding system for needle gauge is as follows:

• Yellow = 30G (e.g. short yellow needle)
  

• Grey = 27G (e.g. long grey needle)
  

• Orange = 25G (e.g. short orange needle)
  

• Brown = 26G (e.g. brown needle)
  

• Blue = 23G (e.g. long grey needle)
  

• Black = 22G (e.g. short black needle) and the
  

• Green = 21G (e.g. 1.5 inch green needle).
  

The diameter of all the gauges is defined with an ISO standard.

Needle bore
The hole down the middle of the needle is known as the bore. In general the bigger the needle, the larger the bore butsome of the finer needles – such as the neversharesyringe – have a smaller bore so that the wall thickness, and strength, can be maintained.


At Exchange Supplies we stock 6 different types of syringe, and the full range of needles.

The syringe types we stock that have been developed by us specially for injecting drug users are the:

• 1ml nevershare all-in-one insulin type syringe
  

• 2ml Nevershare range.
  

The other syringe types we stock are:

• 0.5ml Omnican insulin syringe
  

• 1ml omnican insulin syringe
  

• 1ml Injekt fine dose low dead space syringe
  

• 1ml luer slip syringe
  

• 2ml luer slip syringe;
  

• 5ml luer slip syringe; and
  

• 10 ml luer slip syringe.