PATIKIL 4 Inch Duct Collar, 2 Pcs Duct Connector Flange Galvanized Iron Tight Vent Air Duct Fitting for Heating Cooling HVAC Ventilation Home Office

What I used it for

I put the PATIKIL 4-inch duct collar to work on two small jobs: replacing a tired bathroom fan termination through drywall, and adding a branch pickup to a shop vac/dust-collection line. It’s a simple part—just a short galvanized stub with a corrugated flange—but it solves a surprisingly common problem: transitioning cleanly from a surface (wall, ceiling, cabinet, or panel) to flexible or rigid 4-inch duct without resorting to improvised adapters.

This two-pack came with both collars identical: galvanized steel, a shallow corrugated flange, and a 65 mm (about 2.56 in) insertion depth. The interface outside diameter of the stub measured right at 100 mm (3.9 in) on my calipers; the flange measured just a hair under the listed 115 mm (4.5 in).

Build quality and design

• Material: The galvanized finish is even and uniform. It’s thin enough (about 0.6 mm) to cut or drill easily, but sturdy enough to hold shape under clamp pressure. For reference, that’s roughly equivalent to 24-gauge sheet metal.
• Flange: The “wrinkled” corrugation around the flange isn’t decorative; it adds a bit of spring so the flange sits flush on slightly uneven surfaces and gives the surface sealant some bite. It also makes the flange less prone to oil-canning under screw pressure.
• Edges: The cut edges are crisp. Not dangerously burred, but I still wore gloves. A quick pass with a file on the outside rim makes handling more forgiving.
• Tolerances: The stub being 100 mm OD is just slightly undersized for 4-inch (101.6 mm) flexible duct, which actually helps when inserting into tight flex hose or semi-rigid aluminum. A worm-drive clamp takes up the slack. On rigid spiral duct, the slip fit was snug, not loose.

There are no pre-drilled mounting holes and no gasket included. That’s not unusual for collars in this price bracket, but it’s worth noting so you plan your fasteners and sealant.

Fit and compatibility

• Flex and semi-rigid: 4-inch aluminum flex duct slid on without a fight. With a clamp and foil tape, the joint was airtight.
• Spiral/rigid: On thin-wall metal spiral duct, the stub engages cleanly. I secured it with three short sheet-metal screws (1/2-inch pan heads) and sealed with mastic.
• PVC: The collar will sit inside thin-wall DWV pipe with a bit of play; you’ll need a coupler or a band clamp and gasket to make that a serviceable joint. For schedule 40, it’s too loose for a direct slip fit—expect to use an appropriate adapter.
• Dryer applications: The metal construction and smooth interior are appropriate, but be mindful of code and best practice. Don’t use screws protruding into a dryer vent run; clamp and UL-2158A foil tape are the way to go. The collar itself is fine; how you fasten it is what matters.

If you’re working with 100 mm metric duct (common in some fans and inline blowers), the fit is excellent out of the box.

Installation notes

Here’s the approach that produced the best results for me:

1. Dry-fit and mark: Place the flange on the surface, center it over the cutout, and trace the flange for screw marks. Because the flange is only 4.5 inches across, having at least a 1/4-inch of surface around the hole helps. If your opening is rough-cut, a trim ring or grille will hide the edge.
2. Drill pilot holes: I prefer to drill three or four evenly spaced pilot holes through the flange and the substrate to prevent cracking gypsum or chipping plywood. Self-tapping screws work fine into metal housings.
3. Seal the flange: A bead of mastic or a thin closed-cell foam gasket behind the flange pays dividends. The corrugation compresses nicely and evens out gaps.
4. Fasten lightly, then snug: Get all screws started before tightening to avoid skewing the flange.
5. Connect the duct: Slide the duct onto the stub, clamp it, then seal with foil tape or mastic. On dust collection, I add a second clamp if the line sees vibration.

With the bathroom fan, I also painted the flange edge to match the ceiling trim after install. The galvanization takes paint fine if you scuff it lightly.

Performance in use

This is not a flow-altering component, so “performance” is about sealing, mechanical hold, and longevity.

• Airtightness: After sealing the flange and taping the hose joint, a simple incense smoke test showed no visible leakage. Without sealant behind the flange, I did see faint wisps around the screw locations; the gasket or mastic eliminates that.
• Mechanical hold: The 65 mm insertion depth gives enough purchase for a clamp to bite without slipping off. On the dust-collection branch, the connection has stayed put through repeated on/off cycles and hose movement.
• Noise: Nothing to report. No rattles, and the corrugated flange didn’t introduce any noticeable whistling.
• Corrosion resistance: In a humid bathroom ceiling cavity, the galvanization has stayed clean. After a month there’s no white rust or staining—exactly what I’d expect from galvanized steel.

One clarification: this collar doesn’t include a backdraft damper. If you need to prevent reverse airflow, pair it with an inline damper or an exterior vent hood that has a flap. The collar provides the connection and seal; the damper provides one-way control.

Where it shines

• Tight spaces and retrofits: The undersized 100 mm stub slips into stubborn flex hose and semi-rigid lines without wrestling. That saved me time over crimping a standard 4-inch takeoff.
• Mixed-material transitions: Going from a fan housing or cabinet wall to flex duct is exactly what this is designed for. The flange gives you a clean mounting plane where none existed.
• Humid or splash-prone installs: The galvanized finish is the right call for bathrooms, kitchens, and light-duty shop use.

What could be better

• No pre-drilled holes: I don’t mind drilling my own, but pre-punched slots would speed up installs and standardize the screw pattern.
• No gasket: A thin foam ring would improve out-of-box sealing for folks who don’t keep mastic around.
• Flange diameter: At 4.5 inches, the flange covers a 4-inch hole with a narrow margin. If your cutout is sloppy, plan for a trim plate or grille.

None of these are dealbreakers; they’re trade-offs that keep the part versatile and affordable.

Tips and best practices

• Seal both interfaces: Use mastic or high-quality foil tape at the flange, and clamp + tape on the duct stub. The two-stage seal dramatically reduces leakage.
• Mind the screws: For dryer vents, avoid screws protruding into airflow. For other applications, limit screw length so they don’t snag lint or chips downstream.
• Deburr lightly: A quick file pass on the outer edge improves safety and keeps gaskets from tearing.
• Support the line: Don’t expect the flange to carry the weight of long, unsupported duct runs. Strap the duct within a foot or two of the collar.

Alternatives to consider

• Plastic collars: Easier on the hands and sometimes include gaskets, but they deform under clamp pressure and can yellow or crack near heat sources.
• Spin-in takeoffs with tabs: Better for tapping round trunk lines, but overkill for a wall or cabinet penetration.
• Collars with integrated dampers: Great if you specifically need backdraft prevention, but they add resistance and cost. Pairing this collar with a separate damper gives you choice over damper quality.

The bottom line

The PATIKIL 4-inch duct collar does exactly what a good collar should: it creates a clean, secure, and sealable transition point at a wall, ceiling, or panel and accepts common 4-inch ducting without fuss. The galvanized build is appropriate for HVAC, light dust-collection, and kitchen/bath work; the corrugated flange is a small but thoughtful touch that helps with sealing on imperfect surfaces. You will need to bring your own screws, clamps, and sealant, and if you want a true plug-and-play solution with pre-drilled holes and a gasket, this isn’t that. But once installed correctly, it’s airtight, sturdy, and unobtrusive.

Recommendation: I recommend this two-pack for anyone who routinely connects 4-inch flex or spiral duct to surfaces—bath fans, inline fans, range hoods, light shop pickups, and similar tasks. It’s durable, sized intelligently for real-world duct fit, and easy to seal. If you need an integrated damper or a larger flange footprint, look at specialized alternatives; otherwise, this collar is a dependable, cost-effective staple to keep on hand.