How a precision click-dial pen works: reading the unit counter window and the click

A precision click-dial pen is a tool that measures out liquid using a knob and a set of internal parts. You turn the knob to pick an amount, and the pen moves a plunger (a small rod inside the barrel) exactly the right distance to draw in or push out that volume. Think of it like a measuring syringe with a built-in counter. The Gansulin all-metal reusable pen is a good example, so we will use it to walk through the parts.

Key point: A precision click-dial pen lets you set a precise volume by turning a knob. Each click you feel and hear confirms that one unit has been added or removed.

The dial knob and window

Turning the dial knob spins a small screw inside the pen. That screw turns a number wheel behind the clear unit counter window. The window shows the amount you have set, anywhere from 1 up to 60 units.

One unit equals 0.01 ml on the standard U-100 scale (a common measurement system used in lab work for very small liquid volumes), so 10 units equals 0.10 ml. The window sits at a straight-on angle so you read the number directly in front of you. This cuts down on misreading the number from an angle.

The click you can hear and feel

Each unit has a small groove built into the mechanism, similar to the teeth on a ratchet. As the knob passes each unit, a tiny spring-loaded pin drops into the next groove. This produces a firm bump you can feel and an audible click.

This is very useful at the lab bench. You can count units by touch without ever looking at the window. One clear click is easy to notice even in a noisy room. The confirmation is built right into the hardware, rather than being just a printed scale you have to squint at and trust.

The end-of-travel stop

The dial physically stops turning when you try to set more than what is left in the cartridge. If the knob will not go any further, the cartridge does not have enough liquid to fill that amount.

The pen checks this for you automatically. That is a helpful safeguard compared to a plain syringe, where you have to estimate on your own.

Dialing back without waste

Set too much? Just turn the knob back down. On a well-made pen, dialing the number back down does not push any liquid out. Nothing is lost while you correct your setting.

The Gansulin pen dials all the way back to a 1-unit minimum.

Why metal, and why reusable

• A machined metal body (cut from solid metal rather than molded from plastic) holds its shape and precise measurements far better over time. It also survives years of being stored in a drawer or case.
• The cartridge is the only part you replace, so one pen can take the place of a whole pile of single-use disposables.

See the full pen specifications for dimensions and materials.

Calculations & Reconstitution

Want to work out concentrations and draw sizes for your samples? Our peptide calculator handles the reconstitution and unit math.

Preppin Peppers 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.

Reminder: research and educational reference only. Preppin Peppers 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.

Frequently asked questions

How does the click mechanism work on a precision click-dial pen?

A spring-loaded pin engages successive grooves in the mechanism, one groove per unit, producing a firm tactile bump and audible click each time one unit is added or removed, letting you count by touch without viewing the window.

What does one unit equal in milliliters on a U-100 pen?

On the standard U-100 scale, one unit equals 0.01 ml, so 10 units equals 0.10 ml. The unit counter window on pens like the Gansulin all-metal pen displays settings from 1 to 60 units.

How do you correct an over-dialed setting on a reusable pen without wasting liquid?

Simply turn the dial knob back down. On a well-made pen, dialing down does not expel liquid from the cartridge, so no volume is lost during the correction. The Gansulin pen dials back to a 1-unit minimum.

More in our reusable reconstitution pens collection.

What the research community gets wrong about precision click-dial pens

Click-dial pens are handy at the bench, but a few common beliefs do not hold up. Here is what to keep in mind when you set a volume from a vial or cartridge.

• A click counts a step, it does not prove the volume. Each click means the mechanism moved one unit on the counter. It does not confirm how much liquid actually left the tip. That is why device standards like ISO 11608 test set volume against delivered volume as a separate check.
• "One unit equals 0.01 ml" is a scale rule, not a universal fact. That figure comes from the U-100 marking. It applies to cartridges built to that scale, so do not assume it holds for every liquid you load into a pen.
• Skipping the prime step breaks the math. Air trapped in the cartridge or the needle path means the dialed number and the volume you get can disagree. Priming to clear the air first is what keeps the two in line.
• Accuracy is not equally tight across the whole range. Under the standard, the allowed error band at a 1-unit setting is wider (in percentage terms) than at a mid-range setting. Very small settings carry more relative uncertainty than settings near the middle.
• Metal and reusable does not automatically mean more accurate. Body material and reusability affect durability and feel, not whether a pen meets a tested accuracy spec. Accuracy comes from the device passing the measurement checks, not from what the shell is made of.

From our bench: If you run one of these pens in your lab, we would like your firsthand data. Fill a cartridge with bacteriostatic water, dispense a few set values (for example a low, mid, and high dial setting), and weigh each dispensed drop on an analytical balance to convert mass to volume. Tell us how your measured volumes compared to the dialed settings, whether priming changed the first reading, and how repeatable the numbers were across runs. Share your actual figures and setup, no rounded guesses.

Sources

1. Bacteriostatic Water for Injection, USP , FDA/DailyMed label (0.9% benzyl alcohol)
2. Duerkop et al., Biotechnol J 2018 , Impact of Cavitation, High Shear Stress and Air/Liquid Interfaces on Protein Aggregation
3. Sigma-Aldrich (Merck) , Handling and Storage Guidelines for Peptides and Proteins
4. Klonoff & Nayberg, Factors Affecting Performance of Insulin Pen Injector Technology: A Narrative Review (J Diabetes Sci Technol, 2022) - PMC
5. Dosing Accuracy of Two Disposable Insulin Pens According to New ISO 11608-1:2012 Requirements (J Diabetes Sci Technol, 2015) - PMC
6. ISO 11608-1/-3: Testing pen injectors and insulin pens (dose accuracy, actuation and glide force) - ZwickRoell technical guidance