3 ml glass cartridges explained: the 300-unit standard, seals and storage

3 ml glass cartridges explained: the 300-unit standard, seals and storage

The 3 ml glass cartridge is the workhorse consumable for cartridge pens. It is a small borosilicate glass tube with a crimped metal cap and septum at one end and a sliding rubber plunger at the other. "3 ml" is the fluid capacity; "300 units" is the same volume on a U-100 scale, since 300 units times 0.01 ml equals 3 ml.

A row of 3 ml glass cartridges

Why the format is standard

Because the outside dimensions are standardized, one cartridge format fits a wide range of cartridge pens, including the Gansulin metal pen. That means no proprietary consumables and no lock-in: you can reorder standard 3 ml cartridges without matching them to a single brand of device.

Backlit macro of a 3 ml glass cartridge

The two seals

  • The septum at the capped end is a self-sealing rubber disc behind the metal crimp. A pen needle passes through it, and it reseals afterward.
  • The plunger at the other end is a rubber bung that slides down the glass as fluid is drawn, keeping the contents sealed from behind.

Both seals are what let a cartridge hold a stable volume. A cartridge with a cracked glass body, a damaged crimp, or a torn pouch should not be used.

Individually pouch-sealed

Quality cartridges ship individually pouch-sealed. The pouch is the protective barrier that keeps each cartridge clean and dry until use, so keep cartridges in their pouches until you need them.

Storing sealed cartridges

  • Store in a clean, dry place at moderate room temperature, ideally below 75°F (24°C).
  • Keep humidity moderate; high humidity weakens pouch paper and seal adhesive over time.
  • Keep out of direct sunlight and away from heat sources.
  • Do not use a cartridge whose pouch is torn, wet, or damaged.

To plan how many cartridges a project needs, the supply calculator works it out from your draw size and schedule.

PreppinPeppers sells laboratory hardware and consumables for research, educational, and demonstration use only. This article is general educational information about equipment and does not describe, recommend, or instruct the use of any peptide or other substance in humans or animals. Nothing here is medical advice.