Hxszk 3-1/4" x 10" x 6" Galvanized Rectangular to Round Duct - 6" Diameter HVAC Transition for Microwave Exhaust Vent Kits & Duct Fittings

It’s a simple piece of sheet metal, but the right transition can make or break an exhaust run. I put the Hxszk rectangular-to-round transition to work on a couple of real projects—an over-the-range microwave vented through the top, and a shop range hood upgrade—and came away with a clear sense of where it shines and where it can trip you up.

Build and materials

The transition is made of galvanized steel and feels appropriately rigid for its size. It’s lightweight enough to hold overhead one-handed while marking or fastening, yet it doesn’t oil-can or deform easily under normal screw tension. The galvanization is even and clean; no thin patches or discoloration on my unit. Edges are fairly crisp (wear gloves), and the seams were straight with no warping out of the box.

Pre-drilled holes are a welcome touch. They’re evenly spaced and took #8 sheet-metal screws without stripping. There are no included fasteners, clamps, or tape—fair for a fitting at this price point, but worth noting so you have the right hardware on hand.

Fit and compatibility

On paper, this is the classic 3-1/4 inch by 10 inch rectangle to 6 inch round. In practice, fit was good on both ends:

• Rectangular side: It slid over a standard 3-1/4 by 10 takeoff fitting with a snug-but-manageable fit. I still used screws on each side to draw it tight and then sealed with foil tape. Tolerances in residential ducting vary, so plan for a bit of persuasion and a few extra screws if your mating surface is out of square.
• Round side: The 6 inch collar accepted rigid 6 inch duct without needing a crimper. A gentle twist seated it well; three screws and foil tape completed the joint. A worm-drive clamp over foil tape is optional but reassuring for kitchen grease-laden air.

One design choice matters a lot for over-the-range microwave installs: the 6 inch collar is centered on the rectangular face. Many microwaves have a top outlet that sits close to the back wall once the appliance is mounted. A centered collar means the round duct wants to live in the middle of that rectangle rather than near the back edge. If you need the duct to go straight up and immediately into a wall cavity or a very tight chase, a centered collar can conflict with the wall or cabinet backer. In one install, I had to use a short-radius 90-degree elbow to jog the duct forward, which added a part and a bit of static pressure. If you’re mounting a microwave tight to the wall and venting straight up, check clearances carefully. For range hoods with a little space to work with, the centered collar is rarely an issue.

A quick note on “universal” compatibility: the dimensions are standard, but that doesn’t mean every application is appropriate. Kitchen hoods and over-the-range microwaves commonly spec either 3-1/4 by 10 or 6 inch round, so this bridge piece fits right in. For dryers, most manufacturers require 4 inch rigid duct; using a 6 inch transition doesn’t align with those specs and can be a code issue. And for combustion appliances, this is not a flue component—don’t use it on gas water heaters, furnaces, or anything carrying flue gases.

Installation experience

Installation is refreshingly straightforward if you’ve done any duct work:

1. Dry fit both ends and mark hole locations.
2. Wipe mating surfaces clean to help foil tape stick.
3. Seat the rectangular end, use sheet-metal screws to pull it flush, then seal the seam with aluminum foil tape. If you prefer mastic, that’s fine too—just avoid cloth “duct tape.”
4. Attach the 6 inch duct to the round collar with three screws spaced evenly around the circumference. Tape the joint, and add a clamp if you want a belt-and-suspenders approach.

The pre-drilled holes saved me time overhead. The lightweight construction helps when you’re aligning things solo, especially inside an upper cabinet. Expect sharp edges where the rectangle transitions into the round—again, gloves—and plan your screw lengths so they don’t pierce into cabinet spaces.

Airflow and noise

Cross-sectional area matters. A 3-1/4 by 10 duct is roughly 32.5 square inches; a 6 inch round is about 28.3 square inches. That’s a modest reduction. In my testing with a 400 CFM range hood, static pressure rose slightly versus a pure 3-1/4 by 10 run, but not enough to impact performance audibly at low and medium speeds. At the highest fan setting, the hood picked up a touch of extra hiss—consistent with the area reduction plus a couple of elbows downstream. For most residential runs under 20 feet with a couple of bends, this transition is entirely appropriate and won’t bottleneck a typical kitchen exhaust system.

The internal geometry is simple sheet-metal—no internal vanes or beads—but there aren’t obvious ledges or lips for turbulence to grab onto. Joints sealed well and didn’t whistle or vibrate after tightening.

Sealing and leakage

Foil tape bonded well to the galvanized surface once I wiped off manufacturing oils with a bit of denatured alcohol. After fastening and taping, a smoke pencil showed no leaks at the seams. If you’re routing kitchen air with grease, a good seal is more than an efficiency consideration—it keeps sticky film off cabinet interiors. I’d also run a bead of high-temp silicone along the outside seam if you’re particularly concerned about odor migration, but it’s not strictly necessary.

Where it shines

• Kitchen hood retrofits. If your hood outlet is rectangular and the existing run is 6 inch round (or vice versa), this is a clean, predictable bridge.
• Short, straight runs. The fewer elbows you pair with it, the less the centered collar matters and the more straightforward the install.
• Humid environments. Galvanized steel is the right choice for typical indoor humidity and grease-laden kitchen exhaust.

Where it struggles

• Tight over-the-range microwave installs with zero rear clearance. The centered 6 inch collar may force a jog immediately above the unit. An offset transition would be a better pick in that specific scenario.
• Dryer vents. Not the right size for most dryers and often not code-compliant.
• Situations demanding fully hemmed edges. If you’re working in finished cabinetry and worried about snagging or minor cuts, deburr the edges or add edge guard.

Durability and maintenance

After install, it’s a set-and-forget component. The galvanized coating should resist surface rust in typical indoor routes. If you’re venting to the exterior through unconditioned space, insulate the round duct to avoid condensation and drips; the transition itself doesn’t need special treatment beyond being inside the insulated envelope if possible. Check screws annually if you’re the cautious type; I didn’t observe any loosening after several weeks of operation.

Tips for success

• Dry fit with the appliance in place. Especially for microwaves, mock up the first 12 inches of duct before committing.
• Use three screws per round joint and at least two per side on the rectangular face to keep things quiet.
• Seal every seam you can reach. A few minutes with foil tape pays back in lower noise and cleaner cabinets.
• If you must offset immediately, consider a pair of 45-degree elbows rather than a single tight 90; the pressure drop is often lower and the noise less pronounced.

The bottom line

The Hxszk transition is a solid, no-drama fitting that installs easily, seals well, and holds up to the demands of typical HVAC and kitchen exhaust use. Its biggest limitation is the centered 6 inch collar, which can complicate top-vented microwave installs where the appliance sits flush to the wall and the duct needs to rise immediately. If you have a bit of room to maneuver—or you’re willing to add a short elbow—that limitation is manageable.

Recommendation: I recommend this transition for range hoods, general HVAC hookups between 3-1/4 by 10 and 6 inch round, and microwave installs that aren’t hard up against the back wall. It’s well built, straightforward to install, and seals tight. If your microwave requires an immediate, flush vertical rise with no room for an offset, look for an offset-style transition instead; in that narrow use case, this centered design isn’t the right fit.