Syringe parts, labelled
The labelled parts of a syringe are the needle, barrel, scale, plunger tip, plunger rod, flange and thumb press. The drawing shows a 0.5 mL insulin syringe; a general mL syringe has the same parts with a different scale and, often, a detachable needle.[1]
- Needle. Sized as length × gauge, for example 6 mm × 31G.
- Barrel. Holds the liquid. The scale is printed on it.
- Unit scale. Numbered lines. On this 0.5 mL syringe each line is 1 unit.
- Plunger tip. Line up the thin black line at its top with the mark for the dose. Here it sits on 10.
- Liquid. The measured dose between the 0 mark and the plunger tip: 10 units = 0.1 mL.
- Plunger rod. Pull to draw liquid in, push to inject.
- Flange. Finger grip at the end of the barrel.
- Thumb press. Where the thumb pushes the plunger.
Barrel and scale
The barrel is the clear, calibrated tube that holds the liquid; its scale is printed in units or in mL.[1] Insulin syringe scales are made for one insulin concentration, U-100 or U-40,[2] while BD makes 1 mL barrels with 0.01 mL, U-40 or U-100 graduations.[6] The flange at the end of the barrel is the finger grip.
Plunger: rod, tip and thumb press
The plunger is the moving part: a rod you push with the thumb, ending in a rubber tip that seals the barrel. Insulin instructions call these the Plunger Rod and the Plunger Tip,[4] and the dose is read where the thin black line of the plunger lines up with the scale.[3] See how to read an insulin syringe.
Syringe tip: Luer slip vs Luer lock, and catheter tip
The tip is where the needle or another device attaches, and the main choice is a Luer lock or a slip tip. In BD's line, a Luer-Lok tip is used where a secure connection to another device is needed, while a slip tip is a friction fit that is pushed and twisted into the needle hub.[5]
| Tip | How it attaches | Sizes |
|---|---|---|
| Luer-Lok (Luer lock) | Secure connection to another device | 1–50 mL |
| Luer slip | Friction fit: push and twist into the hub | 1–50 mL |
| Eccentric luer slip | Off-centre tip for work close to the skin | 20 and 50 mL |
| Catheter tip | Long tapered tip for flushing catheters and tubes | 50 mL |
A “Luer lock syringe” is simply a syringe with a Luer-Lok tip; BD offers that tip on every general size from 1 to 50 mL.[5] The sizes are compared in the syringe sizes chart and 3, 5 and 10 mL syringes.
Needle, hub and shield
The needle is sized by gauge and length, attaches through a plastic hub and is covered by a shield until use. BD's needle hubs are colour-coded,[7] and on insulin syringes embecta uses an orange shield for U-100 and a red one for U-40.[2] Gauges, diameters and lengths are in needle gauge sizes.
Low dead space syringe
A low dead space syringe leaves less liquid behind. Dead space is the small volume left in a syringe's tip and needle when the plunger is pushed all the way in. The FDA classifies “low dead space” piston syringes as a separate device type: syringes whose plunger, nozzle and/or needle are designed to reduce medication waste.[1]
Other syringe terms
- cc
- The same volume as 1 mL.[8] ISMP advises writing “mL” instead, because “cc” can be misread as “u”.[9] See cc to mL.
- Gauge (G)
- The size number of a needle; a higher number is a thinner needle. See needle gauge sizes.
- Line value
- How many units or mL one small line represents: ½, 1 or 2 units on insulin syringes, depending on the model.[2]
- mcg and mg
- 1 mg is 1,000 mcg. Write “mcg”, not “µg”, which can be misread as “mg”.[9]
- U-100, U-40, U-500
- Insulin strengths in units per mL, and the syringe scales that match them. See how many units in a mL.
- Unit
- The dose unit for insulin. Write “units”, never “U” or “IU”.[9]
Where to go next: insulin syringe for how insulin syringes are marked, sharps disposal for used syringes, and mg to units for the math.[10]
Frequently asked questions
What are the parts of a syringe?
The barrel with its scale, the plunger (rod, tip and thumb press), the flange, the tip, and the needle with its hub and shield.
What is the difference between a Luer lock and a slip tip syringe?
A Luer lock tip gives a secure connection to another device; a slip tip is a friction fit pushed and twisted into the needle hub.
What is a catheter tip syringe?
A syringe with a long tapered tip that fits catheters and tubes rather than a needle. In BD’s line it comes as a 50 mL syringe used for flushing catheters, gastrostomy tubes and other devices.
What is a slip tip syringe?
A syringe whose tip is a friction fit: the needle hub is pushed and twisted on, with no thread.
What is a Luer lock syringe?
A syringe with a Luer-Lok tip, which gives a secure connection to a needle or another device. BD offers it on every general size from 1 to 50 mL.
What is a low dead space syringe?
A syringe whose plunger, nozzle and/or needle are designed to reduce the liquid left behind after injection, which the FDA describes as reducing medication waste.
Which part of the syringe do you read?
The scale on the barrel, at the thin black line of the plunger tip.
Sources
- Product classification: low dead space piston syringe (product code QNQ, 21 CFR 880.5860)
- Technical data sheet: insulin syringes (Micro-Fine, Ultra-Fine)
- Injection technique guide: how to inject insulin with a syringe
- Humulin R U-500 (insulin human) prescribing information and instructions for use
- BD conventional needles and syringes (product line)
- BD Plastipak 3-piece syringe product family
- BD disposable hypodermic needles: technical data sheet (BD-56356)
- SI units: volume
- ISMP List of Error-Prone Abbreviations, Symbols, and Dose Designations
- Giving an insulin injection