A pen dial counts units, and a unit is a volume - not an amount of material. That number only means something when the cartridge, the fill volume and the concentration are the ones the pen was set up around. Change any one of them and the same dial reading stands for a different quantity, which is exactly where the arithmetic stops lining up.
Which cartridges fit our pens?
- Our pens take standard 3 ml (300-unit) glass cartridges with the 11 mm long plunger (stopper), the cartridge we sell. 3 ml cartridges are also made with a shorter, about 8 mm plunger, and a pen is built for one height, so check that a cartridge from another source has the 11 mm long plunger before loading it; the glass looks identical from the outside.
- Most suppliers never mention this.
- Needles: universal 28G-33G screw-on pen needles.
We test only our own hardware and have not evaluated other manufacturers' pens, so we won't guess how our cartridges behave in them.
What a dispensing pen is
A dispensing pen is a reusable metal device that holds a glass cartridge and uses a turning dial to push out a fixed, repeatable volume of liquid for research use. Each click advances an internal plunger by a set distance, which is what makes successive draws from one cartridge consistent.
Key takeaways
- A pen's plunger moves a fixed distance per dial click, which is why repeated draws from one cartridge stay consistent
- Our pens take standard 3 ml (300-unit) glass cartridges with the 11 mm long plunger (stopper), the cartridge we sell. 3 ml cartridges are also made with a shorter, about 8 mm plunger, and a pen is built for one height, so check that a cartridge from another source has the 11 mm long plunger before loading it; the glass looks identical from the outside.
- Dial units are model-specific — some count device clicks rather than millilitres, so confirm the conversion for your exact revision
- Air pockets in a fresh cartridge can skew the first dial clicks, and reconstitution math has to be right before any dial number means anything
In this article
Which cartridges fit these pens?
Our pens take standard 3 ml (300-unit) glass cartridges with the 11 mm long plunger (stopper), the cartridge we sell. 3 ml cartridges are also made with a shorter, about 8 mm plunger, and a pen is built for one height, so check that a cartridge from another source has the 11 mm long plunger before loading it; the glass looks identical from the outside. Stopper depth is the detail listings leave out — check it before you buy.
Will they fit another manufacturer's pen?
We test only our own hardware, so we can't confirm fit with a third-party device — treat cross-brand compatibility as unverified until that device's maker says otherwise.
All of our reusable peptide pens (V1, V2, V3 and Gansulin) are compared on one page.
What a Dispensing Pen Actually Is
Strip away the branding and it's a simple mechanism: a metal housing holds a 3 ml glass cartridge in place, and a plunger presses against the rubber stopper at the back of that cartridge. Turn the dial and the plunger advances a small, fixed distance, pushing liquid out through the needle end. Because that distance is repeatable, each pull matches the last one — the hand-shake of eyeballing tiny lines on a syringe barrel largely disappears.
Which cartridges and needles fit the pens?
- Our pens take standard 3 ml (300-unit) glass cartridges with the 11 mm long plunger (stopper), the cartridge we sell. 3 ml cartridges are also made with a shorter, about 8 mm plunger, and a pen is built for one height, so check that a cartridge from another source has the 11 mm long plunger before loading it; the glass looks identical from the outside.
- Universal 28G–33G screw-on pen needles.
We can't say how our cartridges behave in another manufacturer's pen, because we have only tested them in our own housing.
How the Dial Turns Into a Real Number
Key point: The pen only measures volume—reconstitution math determines the actual peptide concentration per dial click.
Volume vs. Concentration
Here's the part people skip: the dial only knows volume. It has no idea what's actually dissolved in your cartridge. If you tell it to move 0.1 ml, it moves 0.1 ml whether that liquid is plain water or a solution at any concentration.
So a dial number is a volume increment and nothing more. It carries no information about what is dissolved behind it, and it can't be read as an amount of anything until you know the concentration of the liquid in the cartridge. Same dial setting, two cartridges at different concentrations, two very different amounts drawn.
The Role of Reconstitution Math
The concentration comes from your reconstitution step, not the pen. Reconstitution means adding a measured amount of bacteriostatic water (a saline-based diluent with a preservative in it) to a vial of dry peptide powder to turn it back into a liquid.
If a vial holds 5 mg of peptide and you add 2 ml of diluent, each 0.1 ml drawn out equals 0.25 mg. Change that starting volume by even 0.2 ml and every dial number afterward is quietly wrong, even though the pen itself is working perfectly.
We can't say how our cartridges behave in another manufacturer's pen, because we have only tested them in our own housing.
What the Math Needs From You
Compare
| Input | Where it comes from |
|---|---|
| Volume per dial click | The pen, by design |
| Concentration (mg per ml) | Your reconstitution math: powder mass ÷ diluent volume |
| Amount per click | Volume × concentration |
Get the first two right and the pen executes the math accurately. Get either wrong and it will stay perfectly consistent while reporting a number that no longer means what you think it does.
Pen vs Syringe vs Pipette
None of these tools is wrong — they solve different problems. Here's how they compare for bench work with reconstituted peptides.
Compare
What fits a dispensing pen
Fit is where most pen setups go wrong. Our pens take standard 3 ml (300-unit) glass cartridges with the 11 mm long plunger (stopper), the cartridge we sell. 3 ml cartridges are also made with a shorter, about 8 mm plunger, and a pen is built for one height, so check that a cartridge from another source has the 11 mm long plunger before loading it; the glass looks identical from the outside. Needles are universal 28G–33G screw-on. We haven't tested other manufacturers' pens, so we can't confirm our cartridges work in them — check the cartridge format your pen specifies.
Repeat draws from one cartridge: a pen earns its keep. Calibration-grade records for a written protocol: a micropipette.
What the Research Community Gets Wrong About Dispensing Pens
- Assuming the pen "knows" your concentration. It measures volume only. Mislabel the reconstitution and every dial setting after it is off by the same wrong ratio.
- Assuming every 3 ml cartridge is interchangeable. For our pens, stopper depth decides fit: Our pens take standard 3 ml (300-unit) glass cartridges with the 11 mm long plunger (stopper), the cartridge we sell. 3 ml cartridges are also made with a shorter, about 8 mm plunger, and a pen is built for one height, so check that a cartridge from another source has the 11 mm long plunger before loading it; the glass looks identical from the outside. We have not tested any other manufacturer's device, so we can't speak to fit there.
- Assuming any pen needle fits. Our pens take universal 28G-33G screw-on pen needles; hub and thread still need to match your device.
- Treating dial units as milliliters. Some pens mark dials in device-specific units rather than ml; confirm what one click actually equals on your pen before it feeds any calculation.
- Skipping the prime. Air in the cartridge or delivery path throws off the first click or two.
- Assuming a loaded pen can sit out between sessions. Reconstituted solutions are normally handled under consistent cold storage, and a loaded pen left on a bench adds a variable you did not account for.
Frequently asked questions
Does a dispensing pen measure peptide concentration?
No. It only measures volume. Concentration depends entirely on how much diluent you added during reconstitution, not on the pen's dial.
Is a dispensing pen more accurate than a syringe for research work?
For repeated draws from the same cartridge, yes, because each dial click moves a fixed, repeatable distance instead of relying on reading syringe markings by eye.
What do the numbers on a dispensing pen dial mean?
They represent volume increments set by the device, sometimes in ml and sometimes in device-specific units. Confirm which one your pen uses before relying on it for calculations.
Sources
- Bohannon, Postgrad Med 1999: Insulin delivery using pen devices. Simple-to-use tools may help young and old alike
- Jonker et al., Int J Clin Pharmacol Ther 2021: First pre-filled pen device with highly purified human menopausal gonadotropin (HP-hMG, Menopur) in liquid is shown to be bioequivalent to powder for reconstitution
- Lingen et al., Endocr Connect 2023: Advantages and disadvantages of connected insulin pens in diabetes management
✔ Reviewed by Bryan Le, PharmD, RPh
Bryan is a licensed pharmacist (Doctor of Pharmacy, Registered Pharmacist). Reconstituting lyophilized preparations is core pharmacy practice, so he reviews The Lab’s content for technical accuracy and to keep it within a research-and-education scope, with no medical or dosing advice. View profile on LinkedIn.
Related reading
Related from our lab: the pen · cartridges · bacteriostatic water · reconstitution calculators
Shared by PreppinPeppers for research, educational, and demonstration awareness only. We link to third-party coverage; we do not endorse it, and nothing here is medical advice or a recommendation to use any substance in humans or animals. Our products are sold for laboratory research use only.
Reminder: research and educational reference only. PreppinPeppers sells hardware and materials, not peptides. Not medical, dosing, or health advice, not evaluated by the FDA, and not intended for human or animal use.
