Luer-lock vs luer-slip syringes: which to buy
Buy luer-lock for anything involving a vial: the needle screws on and cannot pop off under the pressure of drawing or pushing liquid, where a luer-slip needle only pushes on. Insulin syringes are neither; their needle is fixed at the factory.
Last edited · written by PepPrep · not medical advice
Both are the standard fitting between a syringe and a needle. The difference is how the needle stays on. Luer-lock screws on; luer-slip pushes on. For anything involving a vial, buy luer-lock.
Why lock
Pulling water through a stopper takes real pressure, and pushing it back into a vial takes more. On a slip fitting that pressure can pop the needle off — usually with the syringe full. A locked needle cannot. The extra cost is pennies per syringe, and every 3 mL and 10 mL syringe we list is luer-lock for this reason.
Where slip is fine
Oral syringes, which have no needle at all, and the syringes sold for measuring liquids for children or pets. If it never meets a needle or a stopper, the fitting does not matter.
Insulin syringes are neither
The needle on an insulin syringe is fixed — glued in at the factory — which is why it can be so thin and why you never swap it. This is the everyday injecting tool; luer syringes are the mixing and transfer tools. The syringes guide puts the whole family side by side.
What fits what
- 3 mL luer-lock syringes + 18G blunt fill needles: drawing and transferring water.
- 10 mL luer-lock syringes: drawing several millilitres at once.
- 27G luer-lock needles: the injecting needle for a luer syringe, if you are not using an insulin syringe.
- Luer-lock tip caps: sealing a filled syringe for a few hours.
- Vial adapters: a spike that sits in the stopper with a luer-lock on top, so no needle is needed to draw.
Which to choose
- Luer-lock for mixing, filtering and filling a spray bottle: the needle cannot come off when you push.
- A fixed-needle insulin syringe for injecting small amounts: least dead space, finest needle, one piece.
- Luer-slip for nothing under pressure. It is fine for oral syringes and rinsing, not for pushing liquid through a 0.22 µm filter.
The catalogue carries no luer-slip syringe, for the reasons above. To see a luer-lock syringe and a fixed-needle insulin syringe with every recorded specification side by side, open them in the comparison tool. The glossary entry has the short definition.
Common questions
Can a luer-slip needle fit a luer-lock syringe?
Physically yes: it pushes on without engaging the thread, so it can still pop off. Use luer-lock needles on luer-lock syringes.
What does "luer" mean?
It is the standard taper on syringe tips, named after its 19th-century inventor. Every luer needle fits every luer syringe of the same type.
Supplies mentioned: Syringes & Needles
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.