Vent Systems 10" Galvanized Steel Duct End Cap - Dryer Vent Cap - Round Metal Plug - Duct Fitting/Tee Cap - Indoor and Outdoor Use – Closure Fitting for Round HVAC Exhaust Systems

A cap for round ducting is the sort of part you don’t think about until there’s an open run whistling in a utility room or a critter path into the attic. I put the Vent Systems 10-inch galvanized end cap to work on a few jobs—sealing an abandoned return branch in a basement plenum and blanking off a redundant roof duct—and it did exactly what a good closure fitting should: seat firmly, seal cleanly, and stay put without drama.

What it is and what it’s for

This is a round, galvanized steel end cap designed to close off standard 10-inch class duct runs. More precisely, it’s sized to insert into ducts with an internal diameter around 9.80 inches, and it has a 2.20-inch flange depth—enough bite to feel secure even before you seal or screw it. The end face measures about 10.24 inches across. It’s a male-style plug: it goes inside the duct, not over it.

Use cases are straightforward:
- Terminating unused branches in a supply or return trunk
- Temporarily capping lines during system balancing or renovation
- Closing off a decommissioned vent penetration
- Shutting a roof or wall penetration while you plan a permanent fix

It’s not a replacement for a code-compliant termination cap on an active appliance. Don’t cap a live exhaust (dryer, water heater, furnace, range hood) with this—or anything else—unless you’ve decommissioned that run. For idle lines, though, it’s exactly the right tool.

Installation and fit

The fit is the make-or-break on a part like this, and the cap’s geometry is well thought out. The shallow side groove helps guide it into a spiral or snap-lock duct without catching a seam, and the flange depth gives you room to work sealant, tape, or screws.

A few practical notes from my installs:
- Measure the inside diameter of the duct you’re capping. “10-inch” is a nominal size, and field conditions vary. If your duct is a true 10-inch OD with a rolled female end, this cap is meant to slip inside that female opening. If you were expecting a cap that goes over the outside of the pipe, this isn’t that part.
- For clean seating, deburr or round any mashed edges with pliers. A gentle twist and push set the cap flush for me in both spiral and snap-lock sections.
- As a friction fit, it held snugly even before sealant. For a permanent cap, I like three 1/2-inch self-tapping screws spaced evenly around the circumference, followed by mastic and/or foil HVAC tape. If you need it to remain removable, skip the screws and use a bead of butyl or silicone you can cut later.

There’s no factory gasket. I prefer that—it lets me choose the right seal: water-based mastic for mechanical rooms, high-temp silicone for roof penetrations, or butyl tape plus foil tape where I want a reversible seal. With a thin bead and a twist, I got an airtight closure and zero rattle.

Build quality and corrosion resistance

The galvanized finish is consistent and the cap arrived true and round. The steel is rigid enough that it doesn’t oil-can with light pressure, which matters on larger diameters. It handled light mallet taps without deforming the face. Edges are typical of stamped galvanized fittings—clean, but sharp—so wear gloves.

The manufacturer calls the galvanization “C2 class,” which in practical terms means it’s suitable for indoor environments and mild outdoor exposure (think under eaves or on a dry roof away from salt spray). For coastal or industrial environments, I’d still use this cap but would overcoat the exposed face with a compatible paint or a bituminous flashing to extend life. On a test roof cap, it shed water fine and showed no discoloration after weather, but long-term corrosion resistance always depends on exposure and maintenance.

Performance in use

Sealing performance comes down to two things: a solid mechanical fit and a continuous air barrier. With a thin mastic bead, the cap stopped airflow on a manometer check and immediately improved static pressure readings in the trunk where I removed an underperforming branch. The result is more than comfort—closing off unnecessary runs reduces leakage and can materially improve system efficiency.

Noise-wise, it’s quiet. I encountered no ringing or buzzing on startup, which can happen with thin or poorly seated caps. The face stayed flat, and the 2.20-inch engagement kept it steady.

As a pest barrier, it’s only as good as your seal. On an attic penetration where insects had found their way in through a tired old cap, a tight install on sound ductwork ended the problem. If your duct end is ragged, ovalized, or corroded, fix the termination or use a short coupling to restore a true round before you plug it.

Sizing realities and expectations

Here’s the most important fit note, because it trips people up: this cap inserts into a “10-inch” duct; it does not sleeve over the outside. If your application requires a cap that goes around the pipe (female to male), you’ll need a different style, typically labeled as a “female end cap” or a “draw band cap.” If your duct is slightly out-of-round, you can re-round it with a hand seamers or a coupling before inserting the cap. For a very tight duct, a tiny crimp at three points can help, but most 10-inch spiral/snap-lock I’ve seen accepted the cap without modification.

Metric equivalence is close to 250 mm. If you’re working on older or mixed systems, confirm with a tape or calipers; a 1/8-inch variance in round can make the difference between finger-tight and mallet-tight.

What I liked

• Proper engagement length: The 2.20-inch flange gives you room for sealant and screws without crowding the face.
• Clean insertion: The side groove and smooth edge roll-in made installs easy even at awkward angles.
• Versatile sealing options: No fixed gasket means I can tailor the seal to the environment—mastic, silicone, butyl, or just foil tape for a temporary close.
• Solid, true round: It stayed round and flat under normal jobsite handling and light persuasion.

What could be better

• No gasket out of the box: That’s a plus for me, but if you want a plug-and-go airtight cap without additional materials, this isn’t that. Expect to use sealant or tape.
• Limited guidance on sizing in the packaging: A simple “male insert cap—fits inside 9.80-inch ID duct” note would help prevent the common over-vs-insert confusion.
• Edge finishing: Gloves are a must; a slightly softer edge break would improve handling.

Tips for a clean, code-friendly install

• Never cap an active combustion or dryer exhaust. Decommission first, and follow local code for permanent closures.
• Clean the duct interior lip before capping. Dust and residual mastic compromise adhesion.
• For permanent indoor caps, screws plus mastic is the most robust combination. For serviceable caps, use a continuous butyl bead and wrap with foil tape so you can cut it later.
• On exterior penetrations, pitch the face slightly or use a bead that sheds water; then overwrap with UV-rated foil tape or flashing for extra protection.
• Label the cap with a marker (e.g., “Unused return branch—2025”). Future you will thank you.

The bottom line

The Vent Systems 10-inch galvanized end cap is a straightforward, well-made insert cap that does its one job reliably: closing round duct runs so they’re airtight, quiet, and weather-resistant. Installation is easy if you understand that it’s designed to go inside the duct, not over it. You’ll need your own sealant or tape, but that flexibility is a virtue in mixed environments, and the generous flange depth makes for a secure, confidence-inspiring fit.

Recommendation: I recommend this end cap for anyone needing to terminate 10-inch class round ducts, provided you confirm the insert style is appropriate for your run. It’s sturdy, seats cleanly, and—paired with the right sealant—yields a durable, airtight closure indoors or in mild outdoor conditions. If you’re looking for an over-the-pipe cap with an integral gasket, look elsewhere; if you want a dependable, no-nonsense insert cap you can trust to stay put and stay sealed, this is a solid choice.