A breast pump flange should feel secure against your breast without squeezing, rubbing, or pulling in more tissue than necessary. If you are using the Momcozy V3 Double Electric Breast Pump, the starting point is its 24 mm DoubleFit™ flange and the smaller inserts supplied in the box. But the best fit is not decided by the number printed on an insert alone. It depends on your measurements, how your nipple moves while pumping, and whether the setup remains comfortable throughout the session.
This Momcozy V3 flange size guide walks through the V3-specific parts, measuring both sides, choosing inserts, installing them, and checking fit. It is intended to help you make a more informed first choice—not to replace individualized advice from an IBCLC, midwife, or other qualified healthcare professional.
Quick Answer:What is the right flange size for the Momcozy V3?
The Momcozy V3 includes a 24 mm DoubleFit™ flange and 17 mm, 19 mm, and 21 mm inserts. To choose a starting size, measure each nipple separately with the V3 sizing ruler, then check how the nipple moves and feels during a comfortable pumping session. The left and right breasts may need different insert sizes; the measurement alone does not confirm fit.
V3 Flange and Insert Sizes: What Comes in the Box?
The V3 uses a 24 mm DoubleFit™ flange as the outer flange component. Smaller silicone inserts fit inside that flange to reduce the nipple tunnel opening. According to Momcozy’s V3 product information, the standard package includes a pair of 17 mm, 19 mm, and 21 mm flange inserts, along with a nipple-size ruler. The 24 mm DoubleFit™ flanges are also included.
In practical terms, the 24 mm flange is the base component; the insert creates a smaller tunnel when needed. The insert size refers to the diameter of that tunnel, not the outside diameter of the entire flange. If you use an insert, make sure it is seated evenly inside the V3 DoubleFit™ flange before placing the collection cup
| V3 component | Standard package | What it does |
|---|---|---|
| 24 mm DoubleFit™ flange | Included (pair) | Outer flange that rests against the breast; accepts compatible smaller inserts. |
| 21 mm insert | Included (pair) | Reduces the tunnel opening to 21 mm. |
| 19 mm insert | Included (pair) | Reduces the tunnel opening to 19 mm. |
| 17 mm insert | Included (pair) | Reduces the tunnel opening to 17 mm. |
| 15 mm insert | Listed separately on V3 replacement-parts page | An additional replacement option; not listed as a standard in-box insert. Check the current listing and V3 compatibility before ordering. |
The available sizes and package contents can change by market or product revision. Check the current V3 listing and the replacement-parts page before purchasing an additional insert. Do not assume that an insert made for another Momcozy pump—or another brand—will fit the V3 simply because it has the same millimeter label.
See the Momcozy V3 Double Electric Breast Pump for the current product details, and review the V3-specific replacement options on the official parts listing.
How to Measure for Your Flange
A nipple measurement gives you a useful starting point, but it does not make the final decision by itself. Flange tunnel shape, material, suction level, and the way your nipple responds during pumping all affect fit. For the V3, use the nipple-size ruler supplied with the pump or a reliable millimeter ruler, and measure the left and right sides separately.
A simple measuring routine
- Prepare first. Wash and dry your hands. Measure when your nipple is in a natural, slightly protruded state. Gentle stimulation may help make the nipple easier to measure; do not pinch or stretch it forcefully.
- Measure the nipple, not the areola. Position the ruler across the nipple and record its width in millimeters. Avoid including the surrounding areola. Follow the measurement points shown on the V3 ruler and Momcozy’s current sizing guidance.
- Measure both sides. Record the left and right measurements separately. It is normal for the two sides to differ, and one breast may need a different insert from the other.
- Use the result as a starting point. Compare each measurement with the V3 size guidance and the insert options available for this model. Do not automatically add a fixed number of millimeters or choose the next size up without checking the fit..
- Test while pumping. Start with a comfortable, low suction setting and check how the nipple moves in the tunnel. Reassess if you notice rubbing, pinching, swelling, persistent pain, or unexpectedly poor milk flow.
Why avoid a one-size-fits-all formula? Clinical guidance does not use one universally accepted calculation for every person and every pump. Cleveland Clinic notes that adding a few millimeters can be a starting point for some users, but there is no single formula that guarantees the right fit. A Washington State Department of Health WIC flange guide also emphasizes measuring each nipple and trying nearby sizes while observing comfort and movement. The V3’s included ruler and the fit test should guide the final choice.
Choose a Size for Each Side
You do not have to use matching inserts on both sides. If your left nipple measures differently from your right, assess each breast on its own. For example, you might begin testing a 19 mm insert on the left and a 21 mm insert on the right if those are the closest available starting options for your measurements. That is only a test combination—not a prescription or a guarantee that either size will be right.
Left side
Measure the left nipple and note the result. Select the closest appropriate V3 insert to test, then position the nipple in the center of the tunnel. During pumping, look for smooth movement without persistent friction. If the nipple is compressed against the tunnel wall or becomes increasingly sore, stop and reassess the size and suction setting.
Right side
Repeat the same process for the right breast. Do not choose the right insert simply because it matches the left. The V3 has independent suction adjustment for each side, which lets you tailor suction separately; that feature does not replace correct flange sizing. A comfortable insert and a comfortable suction level are two different parts of the setup.
| Side | Illustrative measurement | V3 insert options to assess |
|---|---|---|
| Left breast | 18 mm (example only) | Compare 17 mm and 19 mm; assess comfort and nipple movement |
| Right breast | 20 mm (example only) | Compare 19 mm and 21 mm; assess comfort and nipple movement |
The examples above are for explaining the comparison process only; they are not a sizing formula or a recommendation that every person with the same measurement should use the same insert. Use the V3 ruler and current model-specific guidance as your starting point, then assess nipple movement and comfort while pumping. If neither nearby option feels comfortable, stop and ask a lactation professional to help assess fit rather than forcing a size choice.
Install the Insert Correctly
A well-chosen insert can still feel wrong if it is twisted, folded, or not fully seated. Before every session, check that the insert and flange are clean, dry, and undamaged, then assemble them carefully.
- Choose the V3 insert size you want to test for that breast.
- Align the insert with the opening of the 24 mm DoubleFit™ flange.
- Press the insert evenly into the flange so it sits flat and securely around the tunnel. Check the full circumference for rolled or folded edges.
- Look through the tunnel to confirm that the opening is round and unobstructed.
- Attach the flange to the V3 milk collector according to the product instructions. Confirm that the parts are fully connected and that no edge is trapped or displaced.
- Center the nipple in the tunnel before starting the pump. Reposition the flange if the nipple is off-center or the breast seal is uneven.
Do not stretch, cut, trim, glue, or otherwise modify an insert to make it fit. Do not combine parts from another pump model unless Momcozy specifically confirms that exact component is compatible with the V3. If an insert is misshapen, torn, or no longer holds its shape, replace it with the correct V3 part.
Check the Fit During Pumping
The most useful fit check happens while the pump is running—not only when the flange is held against the breast before a session. Start with a comfortable suction level. The V3 offers up to 15 suction levels per side and independent adjustment, but stronger suction is not a substitute for a suitable flange. Increase suction only while it remains comfortable.
| What you notice | What it may indicate | What to do next |
|---|---|---|
| Nipple moves gently in the tunnel; no persistent rubbing or pain. | Potentially comfortable fit. | Continue monitoring during the session and check the nipple afterward. |
| Nipple rubs against the tunnel wall or feels pinched. | The tunnel may be too small, or the nipple may be off-center. | Pause, recenter, and reassess size. Try a compatible larger option if needed. |
| A large amount of areola is pulled into the tunnel. | The tunnel may be too large or positioning may be off. | Reposition and reassess with a compatible smaller option if appropriate. |
| Pain, blanching, swelling, cracks, blisters, or bruising. | Fit, suction, or another issue may be causing tissue stress. | Stop if painful; do not push through it. Seek help from an IBCLC or clinician if symptoms persist. |
| Low milk flow or leaking around the flange. | Possible fit or positioning issue; output can also have other causes. | Check centering, seal, insert seating, and suction. Get individualized support if unresolved. |
A comfortable fit is not necessarily the tightest fit. The nipple should have room to move without being squeezed, and the flange should sit securely against the breast. Some light contact with the tunnel wall may occur; what matters is whether movement is smooth and comfortable rather than persistently rubbing or painful. The Washington State WIC Flange FITS™ resource describes a good fit as one in which the nipple gently moves within the tunnel and pumping feels comfortable.
You can also review the clinical signs described by Cleveland Clinic and the fit illustrations in the Children’s Mercy flange-fit handout.
Compatibility and Replacement Questions
V3 flange sizing is model-specific. The V3 uses a 24 mm DoubleFit™ flange with inserts designed for that assembly. Similar-looking parts from another Momcozy breast pump, a wearable pump, or a third-party brand should not be assumed to fit. A matching millimeter label describes a tunnel size; it does not prove that the insert’s outer shape, rim, height, or connection points are compatible.
Can I use a 15 mm insert with the V3?
Momcozy’s V3 replacement-parts listing currently shows a 15 mm insert as a separately selectable replacement option, alongside 17 mm, 19 mm, and 21 mm inserts. The standard V3 package information lists 17 mm, 19 mm, and 21 mm inserts—not a 15 mm insert. If you need a 15 mm option, verify that the listing is still available and explicitly designated for the V3 before ordering.
Can I use an insert from another Momcozy pump?
Do not assume so. Confirm the exact model and part listing. Even when two inserts share the same nominal diameter, their external dimensions and how they seat in the flange may differ. Use V3-specific replacement parts unless Momcozy confirms compatibility for the exact part number.
Where can I buy replacement inserts?
Use the official V3 replacement-parts listing and select the insert size identified for your pump. Check the product title, model designation, size, quantity, and current availability before checkout. If the part selector or compatibility wording is unclear, contact Momcozy support rather than relying on a generic insert listing.
Shop the V3 Double Electric Breast Pump replacement parts and review the main V3 product page for the current product configuration.
For a broader look at Momcozy’s pump range, browse the electric breast pump collection, or visit the V3 experience page to learn more about the V3 system.
When to Recheck Your Flange Size
Your flange fit may change. Nipple size and shape can shift during pregnancy, after birth, as lactation becomes established, and over the course of a pumping journey. A size that once felt comfortable may become less suitable later. Recheck the fit if you develop new rubbing, discomfort, swelling, leaking, or a noticeable change in pumping experience.
It is also worth checking fit when you switch from direct breastfeeding to more frequent pumping, return to work, change your pumping routine, or replace a worn insert. If you are pregnant and measuring ahead of time, treat the result as provisional; your body may change before you begin regular pumping.
Persistent pain is not something you should have to tolerate. Stop or pause a painful session, check positioning and suction, and seek help from an International Board Certified Lactation Consultant (IBCLC) or healthcare professional if discomfort, nipple damage, or concerns about milk removal continue.
Frequently Asked Questions
What flange sizes come with the Momcozy V3?
The standard V3 package includes a 24 mm DoubleFit™ flange and 17 mm, 19 mm, and 21 mm inserts, plus a nipple-size ruler. Package contents can change, so confirm the current product listing for your purchase.
Does the Momcozy V3 come with a 15 mm insert?
The standard package information lists 17 mm, 19 mm, and 21 mm inserts. Momcozy’s V3 replacement-parts listing separately shows a 15 mm insert option. It should be treated as an additional replacement option, not as a standard in-box item.
How do I know whether I need a 17 mm, 19 mm, or 21 mm V3 insert?
Measure each nipple separately with the V3 ruler, then test the closest compatible insert while pumping at a comfortable suction level. Check nipple movement, friction, comfort, and whether excessive areola is drawn into the tunnel. The measurement is a starting point; the pumping fit check helps confirm it.
Can I use different flange insert sizes on the left and right?
Yes. Measure and assess each breast independently. If the left and right sides need different insert sizes, use the corresponding V3-compatible inserts for each side. The V3 also allows suction to be adjusted independently, but suction settings and insert size should be assessed separately.
Can I use Momcozy M5, M6, or another brand’s flange inserts with the V3?
Do not assume compatibility based on brand or millimeter size. The insert must match the V3 DoubleFit™ flange assembly. Use parts specifically listed for the V3 or obtain confirmation from Momcozy for the exact part number.
What should I do if pumping with the V3 hurts?
Pause and check that the nipple is centered, the insert is seated correctly, and suction is comfortable. Rubbing, pinching, swelling, blanching, cracks, or bruising can indicate a fit or suction problem. Do not keep pumping through pain; consult an IBCLC or healthcare professional if symptoms persist.
