Is an 18g a smaller needle than a 25g?
Lets learn the facts. The “gauge” of a needle refers to the thickness of the shaft of the needle. This is the sterile metal portion which has a beveled, sharp tip (or in some cases for industrial uses a blunt tip).
As a gauge number increases, it would make sense to assume a size would get bigger, just like shoe size, right? Well, I have news for you: For a “gauge” size of a needle tip, being either a luer lock (which means it spins on for a secure connection) or a press-on needle, both sizes will have a finer, smaller, thinner needle as the number increases.
What does this mean for selecting a needle size?
Everyone will have their own opinion, but I can safely say needle gauge sizes ranging from 27g to 31g are very commonly seen in the Insulin Syringe category. This will tell you that the needle thickness is very fine and the most gentle and thinnest needles available.
These sizes are commonly used for insulin dependent patients, or those with a need to measure very small amounts of liquid in the smallest syringes for both animal, human; and even scientific or laboratory applications.
The next smallest size syringe bumps up to the 27g 1cc TB syringe and needle. In my opinion, this syringe and needle is very similar to the largest of the Insulin Syringes, but it has the benefit of having a removable needle tip. When I say “largest”, I am referring to the needle thickness or gauge. When comparing: both measure exactly 1cc or 1mL, both have the same 27g needle tip, both tips are ½ inch in length of needle, and the only objective difference I can report is the fact the 27g 1cc TB syringe & needle has a press-on needle which also accepts a luer lock with perfect function and the Insulin Syringe has a fixed needle that is a permanent attachment to the syringe unit. Remember that all true “Insulin Syringes” have a fixed needle tip, and functionally, that means you need to draw up the liquid and dispense it using that very same needle. For laboratory applications, there is no issue with this, but for human or animal use, regarding the topic of comfort, it can certainly be argued that a needle tip that has not passed through a dense rubber butyl stopper is much sharper than one that has. For this reason, when using a 27g, I do personally prefer our TB 1cc syringe and needle rather than any Insulin Syringe. A separate larger gauge needle tip such as a 20 or 21g needle can be used to draw up and measure liquid quickly and accurately, then replacing this measuring tip with the desired 27 gauge.
Moving along to one size larger: the 25 gauge needle.
Notice the numbers are decreasing yet the thickness of the needle is getting thicker. Once we move into the 25 and bigger sizes, the selections will be 3mL and larger when describing the barrel of the syringe. The barrel is the portion of the syringe which holds the liquid. A sterile small cylinder with graduated markings along the plastic exterior allows one to correctly and accurately measure any liquid needed. It should be noted, that the smaller the syringe, the more specifically one can measure– So what does this mean? For most people, its just a fun scientific fact that won’t have much useful application, but when a very minute amount of liquid needs to be measured with accuracy, it is always best to choose the very smallest syringe that meets your requirements. Just imagine the difference between comparing a liquid measurement of a teaspoon versus a measuring cup. Clearly the very small teaspoon would give you the most accurate measurement, and so does any syringe which holds the smaller volume of liquid.
So to continue, the most commonly seen sizes of 3mL syringe and needle range from 20 gauge through 25 gauge. So you think: 20 gauge is a smaller number so the needle must be smaller? Nope. Like we mentioned previously, as the number gets larger, the needle gets smaller or finer. This means the 25 gauge is the next smallest sized needle available in a 3mL syringe, one step down from the largest Insulin Syringe. This should make you consider thick fluids and medications will pass through this needle slowly and with some difficulty in some cases. So what is your solution? Move down to a 23 gauge which is the next size, only slightly larger than the 25 gauge but with a nearly imperceptible difference. A 23 gauge is a very common size, our most common, most popular size available and is large enough to pass any viscosity of fluid without difficulty. The larger sizes from this point are the 22, 21, and 20 gauge. Both the 20 & 21 gauge are large needle tips, very useful for drawing up fluids quickly without damage to rubber stoppers. We have been told and have personally noticed that the very large 18 gauge and larger do cut a rubber stopper in a knife like fashion, sometimes causing bits of the rubber stopper to fall into the vial which it seals. For this reason, we do recommend 20 or 21 gauge needle tips for measuring fluids.
- Insulin Syringes range from 27g to 31g and all have fixed needle tips.
- There is a 27g 1cc syringe with needle which allows for changing the needle tip size.
- 3mL Syringes come in a variety of sizes ranging from 25g the thinnest needle to 20g the thickest needle- that’s big!
- 5mL Syringes function the same as the 1ml and 3ml syringes with removable needle tips. The only difference is the 5mL holds more liquid, thus making the measurement slightly less specific. This means: for the most accurate measurements, one should use the smallest mL or cc available.
- All needle tips with the exception of Insulin Syringes, are interchangeable and can be removed and reattached to a different syringe as needed. This allows for 100% sharp needle tips, and quick measurement of liquids.