Leviton Blank Cover, 1-Gang, WM1B-GY, Outdoor Electrical Box Cover, Weatherproof, Gray

Why I reached for this blank cover

My introduction to the Leviton WM1B-GY blank cover was a straightforward need: retire a few tired outdoor plates and close off a couple of unused single-gang boxes on a detached garage. I wanted something that would actually stay sealed through rain and heat, not warp in the sun, and wouldn’t look out of place against standard gray outdoor boxes. After installing several of these over the past year, I’ve come away impressed by how quietly competent this simple part is.

Design and build quality

This is a single-gang, metal blank cover with a gray finish and a thick, compressible weatherproof gasket. The plate is flat and rigid with clean edges and a consistent finish that matches common gray outdoor boxes nicely. There’s nothing flashy here—just solid metal, proper thickness, and a gasket that actually feels heavy-duty. The plate has enough mass that it doesn’t oil-can or flex when you tighten it down, which helps the gasket form an even seal.

The gasket is the standout. It’s substantial without being so hard that it refuses to compress. It conforms well to minor irregularities on the box flange and holds its shape over time. The cover arrived with the expected mounting screws, which is always helpful when you’re replacing corroded hardware outdoors.

Installation experience

Installation is as simple as this category gets, but a few small steps make a big difference:

• Kill the power and verify the box is dead with a tester.
• Clean the box flange: scrape off old gasket material and dirt so the new gasket seats properly.
• Place the gasket, then align the cover by hand before starting the screws.
• Tighten incrementally and evenly; you’re compressing a gasket, not torquing down a head gasket. Over-tightening can distort softer gaskets and make sealing worse.

On typical single-gang outdoor boxes, alignment was spot on. The screws engaged cleanly without cross-threading. The gasket didn’t bunch up or slide during tightening, which tells me the compression and thickness are well matched to the plate.

A practical tip: if you’re in a humid or coastal climate, a tiny dab of anti-seize on the screw threads makes the next service call easier.

Weatherproofing performance

A blank cover lives or dies by its ability to keep out water, dust, and insects. This one does that well. After multiple storm cycles—soaking rain, wind-driven spray, and high humidity—the interiors of the boxes I sealed stayed dry and clean. The gasket’s compression set has been minimal: it still rebounds and seals when I pull the plate and reinstall it during other maintenance.

Dust and insect ingress is often the real-world failure mode for cheaper covers, especially once UV exposure hardens the gasket. After months of sun, I haven’t noticed the gasket turning brittle or the seal failing around corners. The plate’s finish has also held up; no chalking or premature peeling. I won’t claim it’s impervious to everything, but it’s doing exactly what I want out of a weatherproof blank.

Fit and compatibility

This cover is sized for standard single-gang outdoor boxes. It’s not an in-use or device cover—just a flat blank for out-of-service or reserve openings. Dimensions are what you expect from a proper blank: enough overlap to cover the box opening and gasket, without overhanging awkwardly.

In terms of color, the gray finish blends with common metallic outdoor boxes and conduits. If you’re mixing brands, I found the match close enough that it doesn’t call attention to itself.

Everyday use and versatility

Most of my installs were straightforward closures: capping an old switch location, sealing a junction box that’s now just a pull point, and keeping an expansion box ready for future circuits. I also used one as a base for a small PoE camera mount on a single-gang box. In that scenario, the plate provided a flat, sturdy surface. If you do something similar, remember that any penetrations you add must be sealed carefully around fasteners to preserve weather protection. I pre-drilled and used a small bead of exterior-grade sealant under and around the fasteners; the interior stayed dry through storms.

In short, while this is purpose-built to be a blank, the metal thickness and rigidity give you some flexibility for light mounting tasks without turning the cover into a tin can.

Durability and maintenance

Outdoor hardware fails in two ways: the metal corrodes or the gasket quits. After extended exposure, I haven’t seen rust or corrosion on the plate or screws, and the gasket hasn’t flattened to the point of losing compression. The finish still looks clean, and debris wipes off easily. If you live where sprinklers hit the face daily, an occasional rinse and wipe keeps mineral buildup from attacking any finish over the long haul.

If you ever need to pull the cover and reinstall it, the gasket can be reused if it’s still pliable and intact. I’ve done this a couple of times without losing the seal, though if a gasket ever tears or permanently flattens, I’d replace it rather than try to stretch its life—weatherproofing is the whole point.

Limitations and what I’d improve

• It’s a blank, not a device cover. If you need access or an in-use configuration, this isn’t it.
• There’s no hinge or lock option, which is normal for a blank, but worth noting for security-minded installations.
• Color choice is essentially “utility gray.” It matches typical boxes, but if you’re after architectural finishes, you’ll be painting or looking elsewhere.
• If you plan to mount anything to the face, treat that as a special case: seal penetrations and understand you’re altering the intended function. This isn’t a structural mounting plate.

None of these are faults so much as category realities. For what it’s designed to do, it does it well.

Value and comparison

Pricing is in line with other quality metal blanks, and the included gasket and hardware make it a complete, ready-to-install solution. You can find cheaper covers, but in my experience, the difference shows up in thinner metal, inconsistent finish, and gaskets that harden too quickly or never seat evenly. Paying a couple of extra dollars once is cheaper than replacing a failed cover and dealing with moisture in a box.

Practical tips

• Clean the box flange thoroughly; the best gasket in the world won’t seal against old silicone and grit.
• Tighten screws until the gasket compresses evenly around the perimeter—stop before you see the plate deflect.
• If you’re near salt air or heavy chemicals, consider a light coat of corrosion inhibitor on the screw heads after installation.
• Label the inside of the box if it’s reserved for future circuits. A dry, sealed box is much nicer to revisit months later when you know what it’s for.

Final recommendation

I recommend the Leviton WM1B-GY blank cover for anyone needing a reliable, weather-resistant closure for single-gang outdoor boxes. It’s solidly built, the gasket seals the way it should, the finish holds up outside, and installation is straightforward. In a category where failures are inconvenient and sometimes costly, this one simply does its job and keeps doing it. If you want a dependable blank cover that matches standard outdoor hardware and won’t have you revisiting the same box after the next storm, this is the one I’d put on the truck.