What Is A 3-Part Syringe?

syringe parts


As the phrase implies, a 3-part syringe consists of three essential structures, and these are (1) the barrel, (2) the plunger, and (3) the gasket.

3-part syringe
3-part syringe

With all the parts working together, the 3-part syringe injects a medicine, a biological product, and related substances into the human body—directly or through another device that could be an infusion set.

It is actually a pump equipped with a plunger that fits tightly and ideally in a tube. Pushing or pulling the plunger, a liquid or gas could be drawn in or expelled through an orifice at the open end of the barrel.


syringe parts
syringe parts


This is the cylindrical tube of the syringe wherein the plunger could be pushed in or pulled out. It is made up of polypropylene.


This is the structure inside the barrel, which can be pushed or pulled. If pulled, a liquid or gas will be sucked inside the barrel. If pushed, the fluid or the gas will be expelled. The plunger is also made up of polypropylene.

Gasket (Rubber stopper)

This is the rubberized material that is attached to the lower end of the plunger. It prevents fluid or gas from returning or leaking back while the plunger is being pushed or pulled.

The gasket could be made up of latex or latex-free material. Hence, for patients who are allergic to latex, the latex-free syringe is highly recommended.

Types of syringes

Luer-lock syringes

This syringe-type allows the needle to be twisted onto the tip and is finally locked in place. This ensures that the needle cannot be knocked off or removed if not intended. Thus, this type of syringe prevents accidental removal of the needle while a fluid or a medication is injected. It also ensures that leaking of any liquid being injected is prevented.

luer lock syringe
Luer lock syringes

Luer-slip syringes 

These syringes do not have threading at the tip. They do not have the mechanism of locking the needle. The needle is simply pushed down the Luer-taper tip and fits very snugly.

luer slip syringe
Luer slip syringe

There are two kinds of Luer-slip syringes in tip types: (1) Luer-slip centric and (2) Luer-slip eccentric. In the centric type, the barrel’s opening where fluid or air could enter or exit is located at the center of the bottom end; in the eccentric type, the opening is situated at the peripheral side of the bottom end. The eccentric type is used to puncture the surface vein or artery.


The Luer-slip syringes are used to inject non-oily medications or substances. Not provided with a lock, they cannot withstand the high pressure required by oily substances from the plunger. But having no lock, it is easier and quicker to fit the needle to the syringe tip.

Syringe and the hypodermic needle  

The components of the 3-part syringe are mentioned in the preceding. However, it is worth noting that there is a fourth part that the syringe cannot fully discharge its functions without it. This fourth part is the hypodermic needle. Without the hypodermic needle, the human tissue or the injection site of the infusion set cannot be penetrated. Therefore, the contents of the syringe cannot be transferred to its intended beneficiary.

hypodermic needle
Hypodermic needle

Measurements for syringe and needle

The syringe and the needle work in pairs and together. For the pair to work more efficiently, the nature of the work where they will be used needs to be assessed.

Some of the questions to be answered are: (1) What is the volume of the medication to be used? (2) What route of administration will be used? Is it subcutaneous, intramuscular, or intravenous? What is the age and physical size of the recipient, the patient? Suppose these have been answered, then, before using the syringe and the needle.

In that case, some measurements need to be factored in so that their inherent functions can be discharged most appropriately. These are the measurements that need to be considered in the selection of the syringe and the needle: (1) needle gauge, (2) needle length, and (3) syringe size.

Needle gauge 

This indicates the thinness or thickness of the needle. The lower the gauge is, the wider the diameter of the needle. Thus, the gauge measures the diameter of the needle.

When a small amount of a substance needs to be injected, a higher gauge needle should be used to be less painful. Suppose a larger amount of medication needs to be injected. In that case, a low-gauge needle should be used so that the injection can be accomplished faster. The flow of the drug will be much faster if the diameter of the needle is wider. 

Needle length

The length has to be factored in, too, before deciding to use a particular needle. For subcutaneous injection, wherein the needle has to reach only the area immediately below the skin, a shorter needle can be used. For intramuscular injection, especially for a bigger and stocky body, a longer needle needs to be used.

Syringe size  

The syringe size has to be considered, too, when injecting medication. For example, the syringe volume size could be 1, 2.5, 5, 10, 15 ml. and so on. 

Suppose a 4 ml of medicine will be injected, for example. In that case, it is logical and most appropriate that a 5 ml syringe will be used. However, if a 2.5 ml syringe is used, two injections will be needed to ultimately deliver the 4 ml medication.

On the other hand, if the larger syringe is used, such as 15 ml, volume size, to deliver 4 ml medication. It would be harder to see the 4 ml marking on the syringe barrel. So, the amount of drug injected is very likely either lesser or more than what is needed.    

Care of and precautions for syringes 

· For disposable syringes, never use them after their first use.

· Before using any form of a syringe, inspect the parts and ensure that there are no cracks and other forms of breakages. Also, ensure that there are no grease traces, dust, deformities, and other unwanted materials.

· Ensure that the wrapping of the syringe is not opened and tampered with before using it.

· Before disposing of any form of a syringe, ensure that the plastic cap of the needle is in place and follow the approved disposal procedure of the medical clinic or hospital.

· Store the syringes in a place where the right temperature is available and free from insects that could contaminate them.   

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