Syringes and needles: which one, and why
Two kinds of syringe and the needles that go with them: fixed-needle U-100 insulin syringes for injecting small amounts, where 100 units is 1 mL and 31G is the usual needle on the 0.3 and 0.5 mL barrels, and luer-lock syringes marked in millilitres for mixing and moving liquid, with blunt drawing needles and pen needles alongside. The two are easy to confuse: an insulin syringe's needle is built in, so almost nothing is left behind in the hub, while a luer tip is a screw thread that takes a blunt drawing needle, a filter or a vial adapter.
Insulin syringe or luer syringe: which is which?
On an insulin syringe the barrel matters more than the needle. A 0.3 mL barrel holds 30 units and spreads them over the same length a 0.5 mL barrel uses for 50, so each line sits further apart and a small amount is easier to read. A 1 mL barrel holds 100 units but most brands mark it every second unit, because there is not room for a hundred separate lines. Half-unit versions exist, and they are a 0.3 mL feature. Gauge — the thickness — runs backwards: 31G is thinner than 30G, and the thinner needles come on the smaller barrels.
On a luer syringe the question is the connection and what you screw into it. Luer-lock has a threaded collar the needle screws into and cannot pop off under pressure, which is what you want pushing liquid through a 0.22 µm filter or into a spray bottle. Blunt fill needles are wide and deliberately dull for drawing up quickly; they are still sharps and still go through skin under force, and they are never for injecting. Pen needles belong to neither group: they screw onto a pen's own thread and are the one consumable a pen routine eats.
What differs between listings
- Gauge is the needle's thickness. A higher number is a thinner needle: 31G is thinner than 30G.
- Capacity is how much liquid the barrel holds. Smaller barrels have more space between the lines, so small amounts are easier to read.
- Smallest line is what one line on the barrel is worth. Half-unit lines let you read 0.005 mL; a 1 mL syringe is usually marked in 2-unit steps.
- Needle length is how long the needle is. 4–8 mm (5/32–5/16 in) is common for under-the-skin use, and 13 mm (1/2 in) insulin syringes are used under the skin too; muscle needles are usually 25 mm (1 in) or longer.
- Whether a needle is included at all: luer syringes usually ship without one.
- Needle length, which is separate from gauge: 4 to 8 mm is the usual under-the-skin range, 12.7 mm (1/2 in) is an older under-the-skin length, and needles for muscle are typically 25 mm (1 in).
Recorded specifications compared
Values come from each product's own record; a dash means the record has none for that column.
| Product | Type | Gauge | Capacity | Markings | Smallest line |
|---|---|---|---|---|---|
| Insulin Syringes 31G, 0.5 mL (100-count) | Insulin syringe | 31G | 0.5 mL | U-100 | 1 unit |
| Insulin Syringes 31G, 0.3 mL (100-count) | Insulin syringe | 31G | 0.3 mL | U-100 | 1 unit |
| Insulin Syringes 30G, 1 mL (100-count) | Insulin syringe | 30G | 1 mL | U-100 | 2 units |
| Luer-Lock Syringes, 3 mL | Luer syringe | — | 3 mL | mL | 0.1 mL |
| Blunt Fill Needles, 18G | Needle | 18G | — | — | — |
| Pen Needles 32G (100-count) | Pen needle | 32G | — | — | — |
| Half-Unit Insulin Syringes, 0.3 mL | Insulin syringe | 31G | 0.3 mL | U-100 | 0.5 unit |
| Luer Needle Tips, 27G | Needle | 27G | — | — | — |
| 10 mL Luer-Lock Syringes | Luer syringe | — | 10 mL | mL | 0.2 mL |
Everything in Syringes & Needles (12)
- Insulin Syringes 31G, 0.5 mL (100-count)31GU-1000.5 mL0–50 units
- Insulin Syringes 31G, 0.3 mL (100-count)31GU-1000.3 mL0–30 units
- Insulin Syringes 30G, 1 mL (100-count)30GU-1001 mL0–100 units
- Luer-Lock Syringes, 3 mL3 mLLuer-lockNo needle
- Blunt Fill Needles, 18G18GBlunt tipLuer-lock
- Pen Needles 32G (100-count)32G4 mm100-count
- Sterile Syringe Caps (100-count)Luer-lock100-count
- Half-Unit Insulin Syringes, 0.3 mL31G0.3 mL½-unit marks
- Luer Needle Tips, 27G27GLuer-lock
- Syringe Magnifier ClipClip-onDoubles the markings
- Lighted Magnifying Glass3× to 10×LED litBattery
- 10 mL Luer-Lock Syringes10 mLLuer-lock tipSterile, wrappedNo needle
Narrow this category by specificationCompare side by side
Written comparisons
Guides for this shelf
- Syringes and needles, translated
- 0.3, 0.5 or 1 mL insulin syringe: which size to buy
- Needle gauge chart: 18G to 32G, and what each is for
- Insulin syringe units to mL: conversion chart
Last edited . Equipment only: nothing on this page is advice about what to inject, how much, or whether a product is fit to use. That comes from the product's labelling and whoever supplied it. Product pages link to your own country's Amazon store through affiliate links; your price is the same.