Understanding Inner & Outer Needle Diameter

Understanding Inner & Outer Needle Diameter

Understanding Inner & Outer Needle Diameter

Understanding the inner and outer diameter of a needle is critical to choosing the right product for your specific application. You’ll also want to consider the gauge, length, needle wall type, and brand.

Needles come in various gauges, and their inner diameters can also vary depending if they have a(n):

  • Regular wall
  • Thin wall
  • Extra-thin wall
  • Ultra-thin wall

These many factors can complicate the process of choosing the correct needle. Read on to learn more about the ins and outs of different needles.

What Is the Outer Diameter of a Needle?

The outer diameter refers to a needle’s gauge (abbreviated as “g”). The higher the gauge number, the smaller the outer diameter of the needle (and the thinner it appears). Smaller needle gauges help produce less bleeding and bruising, making injections more comfortable for patients. 

What Is the Inner Diameter of a Needle?

A needle’s inner diameter describes the size of the needle’s lumen (the hollow bore that runs the length of a needle). Injectables have various consistencies, and thicker fluids cannot flow through smaller lumens. Because of this, viscous material passes more easily through a needle with a larger inner diameter. 

Needles with larger lumens also offer a better flow rate and require less extrusion force, which is the amount of pressure needed to push the material through it. 

What Is the Needle Wall?

The terms, “regular wall,” “thin wall,” “extra-thin wall,” and “ultra-thin wall” describe the thickness of the needle wall. Needle wall thickness is based on the inner and outer diameter. A needle’s gauge defines the thickness of the outside diameter. But the thickness of the needle wall itself can also vary (regular, thin, etc.), which affects the size of the lumen inside.


When to Choose a Thin Needle Wall

A thinner needle wall allows you to maximize flow rate while minimizing needle gauge size. This provides a more comfortable injection for the patient.

For example, 30g needles with an ultra-thin wall have a similar-sized lumen to: 

  • 25g regular wall needles
  • 27g thin wall needles
  • 29g extra thin wall needles

When to Choose a Thick Needle Wall

On the other hand, a thicker needle wall provides additional sturdiness and stiffness. Due to the added thickness, long needles with a regular wall are less likely to flex than those with thinner walls. A thicker wall may also dull less quickly than a thinner-walled needle.

Universally Accepted Standards of Needle Dimensions

Gauge DESIGNATED METRIC SIZE (mm) OUTER DIAMETER MIN (mm) OUTER DIAMETER MAX (mm) WALL TYPE INNER DIAMETER MIN (mm)
14 2.1 1.95 2.15 Regular
Thin
Extra Thin
1.500
1.600
1.727
15 1.8 1.75 1.9 Regular
Thin
Extra Thin
1.300
1.460
1.560
16 1.6 1.6 1.69 Regular
Thin
Extra Thin
1.100
1.283
1.390
17 1.4 1.4 1.51 Regular
Thin
Extra Thin
Ultra Thin
1.24
1.276
.790
.950
18 1.2 1.2 1.3 Regular
Thin
Extra Thin
1.156
1.244
1.276
19 1.1 1.03 1.1 Regular
Thin
Extra Thin
Ultra Thin
.850
.891
.560
20 0.9 0.86 0.92 Regular
Thin
Extra Thin
Ultra Thin
.687
.713
.490
21 0.8 0.8 0.83 Regular
Thin
Extra Thin
Ultra Thin
0.49
0.547
0.610
0.645
22 0.7 0.698 0.73 Regular
Thin
Extra Thin
0.390
0.440
0.522
23 0.6 0.6 0.673 Regular
Thin
Extra Thin
0.317
0.370
0.460
24 0.55 0.55 0.58 Regular
Thin
0.280
0.343
25 0.5 0.5 0.53 Regular
Thin
.232
.292
26 0.45 0.44 0.47 Regular
Thin
232
.292
27 0.4 0.4 0.42 Regular
Thin
.184
.241
28 0.36 0.349 0.37 Regular
Thin
.133
.190
29 0.33 0.324 0.351 Regular
Thin
Extra Thin
Ultra Thin
.133
.190
.240
.265
30 0.3 0.298 0.32 Regular
Thin
Extra Thin
Ultra Thin
.133
.165
.190
.240
31 0.25 0.254 0.267 Regular
Thin
Extra Thin
Ultra Thin
.114
.125
.146
.176
32 0.23 0.229 0.241 Regular
Thin
Extra Thin
Ultra Thin
.089
.105
.125
.146
33 0.2 0.203 0.216 Regular
Thin
Extra Thin
.089
.105
.125
34 0.18 0.198 0.191 Regular
Thin
Extra Thin
.064
.091
.105
*Consideration can be made to the measurement uncertainty of existing measurement equipment for needle sizes below 0.25mm

Needle Diameter: Frequently Asked Questions

At Air-Tite, we often hear questions regarding needle sizes such as:

  • What is the thinnest needle Air-Tite offers?
  • Which needle has the smallest diameter?
  • What is the smallest needle?
  • Which gauge needle is the smallest?

However, these questions may not be specific enough to get the information you need to select the best product. 

For instance, when asking which needle has the smallest diameter, it’s important to specify whether you’re referring to the inner needle diameter or outer needle diameter. The outer diameter (the gauge) reflects how thin the needle appears when viewed by the naked eye. But ultimately, the inner diameter varies based on needle wall thickness.

Additionally, by asking about the smallest needle, you could be referring to the smallest gauge or the shortest needle length. That’s why you must clarify the characteristics you’re inquiring about.

Fortunately, Air-Tite offers several options for those looking for super thin needles. THE INViSIBLE NEEDLE™ is the thinnest needle TSK Laboratory has ever made. At just 0.2mm in diameter, it’s 33% smaller than a 30 gauge needle, making it even smaller than a 33 gauge needle. THE INViSIBLE NEEDLE™ also features the product-saving Low Dead Space needle hub, differentiating it from other needles on the market. 

Looking for additional options? Air-Tite offers 34 gauge standard hub needles from JBP in various lengths to suit your needs.

Shop Air-Tite Needles and Syringes

Understanding needle diameters and needle wall thicknesses help you make an informed purchase. At Air-Tite, we carry a wide range of needles, syringes, and associated products to ensure the best surgical experience and outcome. Click below to learn more.

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