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We make both kinds at our factory. And we've watched people curse at both kinds.
Flange-mounted vent has a lip that sits on the outside of the cabinet. Bolt-on is flat – you drop it in the hole and screw it down.
Which one sucks less? Depends. Here's what we've seen.
Flange – Seals Easy, Looks Clean
The flange is a raised edge around the vent. It overlaps the cabinet wall. Gasket goes behind it. Screw through the flange into the cabinet.
Good parts:
Sealing is forgiving. Your cutout doesn't have to be perfect – the flange covers the sins.
Gasket stays put. Sandwich between flange and wall.
Hides rough edges. Looks professional.
Bad parts:
Takes more space outside. Flange sticks out.
Costs more. More metal, more machining.
Dust can collect on the lip.
When to use: Outdoors. Retrofit jobs where the hole is ugly. When sealing is critical.
Bolt-On – Saves Space, Cheaper
Bolt-on vent is flat. Slides into the cutout. Screws go through the frame into the cabinet. No lip.
Good parts:
Flush mount. Doesn't stick out.
Cheaper. Less metal, simpler to make.
Easy to clean – no lip for dust.
Bad parts:
Cutout has to be damn precise. Any gap leaks.
Thin cabinet metal? Screws strip easy.
More room for installer error. Warp the frame, leak.
When to use: Indoors. Tight spaces. Budget jobs.
Sealing – Flange Wins Hands Down
Flange is forgiving. Your cutout can be a little big, a little wonky – flange covers it. Gasket compresses even.
Bolt-on needs a perfect cutout. Clean edges. Flat surface. Any gap around the frame is a leak. We've seen bolt-on vents on warped doors – tighten the screws, frame bends, gasket lifts, RF leaks. Flange wouldn't have that problem.
Installation Time
Bolt-on is faster if the hole is right. Drop it, run screws, done. Five minutes.
Flange takes longer. Align the flange, more screws, fuss with gasket.
But fixing a leak on a bolt-on? That's a headache. Retorque, maybe recut the hole. So flange is slower first time, but less hassle later.
Space
Flange adds about half an inch to an inch on each side. If your cabinet is crammed against a wall or another cabinet, that's a problem.
Bolt-on is flush. Good for tight racks.
We had a customer with telecom cabinets lined up side by side. Flange vents would have touched. Bolt-on fit fine.
Cost
Flange costs about 20-30% more. More material, more machine time. Bigger gasket.
Bolt-on is cheaper. For large production runs, that adds up.
But if you get leaks and have to rework, the savings disappear.
Real Example – Outdoor 5G Box
Outdoor base station. Cutouts were punched, not machined – rough edges. They tried bolt-on first. Leaked at corners. Switched to flange. Flange covered the mess. Sealed perfect. They stayed with flange.
Real Example – Data Center Rack
Server racks back to back. No room for flange. Bolt-on flush mount worked fine. Low RF inside. Sealing wasn't critical. They saved money.
Which One?
Cutout sloppy? Sealing critical? Outdoor? Flange.
Space tight? Budget tight? Indoor? Bolt-on.
Flange seals easier, hides ugly holes, costs more, takes space.
Bolt-on is cheap, flush, space-saving, but needs perfect cutout and careful install.
We make both. Not sure? Send us a picture of your hole. We'll tell you which one won't leak. That's what we do.