U-40 vs U-100: why are the syringe scales different?

U-40 and U-100 specify concentration, not barrel volume. U-40 is calibrated for 40 units per mL. U-100 is calibrated for 100 units per mL. Both scales are offered in 0.5 mL and 1 mL barrels.

Key specifications compared

Why the scales differ

A piston syringe uses a calibrated hollow barrel and a movable plunger. FDA lists insulin syringes under product code FMF, regulation 21 CFR 880.5860. The FDA classification record does not create separate device types for U-40 and U-100; the distinguishing property is the barrel calibration.

As reproduced in Médecins Sans Frontières’ procurement specification for ISO 8537, an insulin syringe indicates the concentration it is intended to contain, and its scale is graduated in units of only one concentration. The barrel is also marked with that concentration. U-40 and U-100 are therefore different printed calibrations, even where the nominal barrel capacity and needle dimensions match.

Wenzhou Wuzhou’s FDA 510(k) summary lists 0.5 mL and 1 mL syringes in both concentrations. Allison Medical shows the same product pattern in matched rows: a 1 cc, 29G × 1/2" barrel appears as item 12-4910 on the U-40 scale and item 12-7910 on the U-100 scale, with different UPCs. Their 3/10 cc and 1/2 cc syringes also share the 29G × 1/2" needle dimensions. UltiMed’s catalogue shows the same pairing across its two product lines: the 1 cc, 29G × 1/2" barrel is item 09261 in the animal-health line on the U-40 scale and item 09219 in the consumer line on the U-100 scale.

UltiMed lists its U-40 syringes under animal health and its U-100 syringes under consumer health — the two catalogue paths are literally /animal-health/ and /consumer-health/. Banfield’s listing for the UltiCare VetRx U-40 line carries the notice “For animal use only”. That is why the U-40 references here are veterinary catalogues.

Nominal capacity and unit scale are separate fields. A capacity label does not identify the concentration scale. The product record also matters: Allison Medical item numbers distinguish near-identical variants, while UltiMed publishes gauge and needle length as fixed pairs. Its U-100 grid lists no 31G × 12.7 mm or 28G × 6 mm combination.

UltiMed lists its 1.0 mL U-100 syringe at 2-unit increments, while MSF lists 1 IU or 2 IU. U-40 listings state whole-unit markings and identify half-unit options. Red and orange cap colours correspond to U-40 and U-100 respectively. The printed concentration remains the explicit barrel identifier.

Sources

• eCFR — 21 CFR 880.5860, Piston syringe
• FDA — Product Classification database, product code FMF
• Médecins Sans Frontières — UniCat insulin syringe specification
• FDA 510(k) K110421 — Wenzhou Wuzhou Import & Export Co., Ltd., Disposable Insulin Syringe
• Allison Medical, Inc. — CarePoint Vet U-40 and U-100 data sheet
• UltiMed, Inc. — UltiCare U-100 Insulin Syringes
• UltiMed, Inc. — UltiCare VetRx U-40 Insulin Syringes
• UltiMed, Inc. — UltiCare VetRx U-40 Insulin Syringes, 3/10cc 29G × 1/2", Half Unit Marking (product page)
• UltiMed, Inc. — UltiCare VetRx U-40 Insulin Syringes, 1cc 29G × 1/2" (product page)
• UltiMed, Inc. — UltiCare U-100 Insulin Syringes, 1 mL/cc 12.7mm × 29G (product page)
• Banfield Pet Hospital — UltiCare VetRx U-40 Insulin Syringes
• Banfield Pet Hospital — UltiCare VetRx U-100 Insulin Syringes

Specifications last verified: 2026-07-31