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Luer-lock vs luer-slip syringes: which to buy

Lock screws on, slip pushes on. For anything involving a vial, lock. Where slip is fine, why insulin syringes are neither, and what fits what.

Last reviewed · 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

Supplies mentioned: Syringes & Needles

What you'll need

Luer-Lock Syringes, 3 mLSyringes with a threaded tip that needles (and filters) screw onto…10 mL Luer-Lock SyringesBig sterile syringes with a screw-on tip. For drawing several…Blunt Fill Needles, 18GWide, deliberately blunt needles that screw onto a luer-lock syringe…Luer Needle Tips, 25–30GBoxed sterile needle tips that screw onto luer-lock syringes, in a…Sterile Syringe Caps (100-count)Little screw-on caps that seal the tip of a luer-lock…Vial Adapter SpikesPlastic spikes that seat onto a vial's stopper once and give it a…

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