KK magsun 4 Packs Square Electrical Box Cover with 1/2 Inch Knockout, 4 Inch Metal Junction Box Covers, Flat Outlet Box Plate with Angled Mounting Slots for 4 inch Square Box

Why I reached for this cover

I keep a bin of “no-drama” parts in the shop—things I can trust to just solve a problem and let me get on with the job. The KK magsun square box cover has earned a spot in that bin. It’s a simple 4-inch flat cover for metal junction boxes with a 1/2-inch center knockout and angled mounting slots. On paper, that doesn’t sound like much. In practice, it’s exactly the kind of tidy hardware that saves time during service calls and cleanup work.

I used this four-pack across a handful of tasks: closing off abandoned junctions in a garage, finishing a basement run where a box needed to stay accessible, and tidying up an old work ceiling box with a slightly crooked mounting ear. The common thread was speed, clean results, and no surprises.

Build quality and feel

These covers are stamped from galvanized steel and feel appropriately stout. They don’t oilcan under light pressure, and the edges are neatly deburred—important when you’re working overhead or in tight spaces. The galvanization is uniform, with that “utility” silver finish you expect. They’re not dressed up for a living room wall, but they’re absolutely appropriate for basements, shops, garages, and utility rooms. If you do want a more finished look, the surface takes primer and paint without fuss; I scuffed one with a Scotch-Brite pad, primed it, and it finished cleanly with a rattle-can enamel.

I didn’t measure the exact thickness, but stiffness is comparable to the better covers from major electrical brands. None of the four plates came warped, and once tightened they pulled flush without any corner lifting.

Installation: the angled slot advantage

The standout feature here is the angled mounting slots. They’re cut as elongated keyholes, oriented to give you up to about 12 degrees of forgiveness. That has two benefits:

• You can leave existing box screws in place and slip the cover under them. That’s handy in old boxes where the screw threads are tired, and repeated removal/reinstall risks stripping the stamped threads.
• You can compensate for slightly misaligned box ears. I had one box in plaster that wasn’t perfectly square to the wall; with straight slots, you’d often fight the screw alignment. With these, I could set one screw snug, swing the plate into position, and cinch the other without cross-threading.

If you haven’t used slotted covers before, the move is simple: back out the existing 8-32 machine screws a couple of turns, align the slots over the screw heads, slide, then tighten. If you don’t have screws in the box, plan on supplying your own; these covers don’t include hardware. I used 8-32 x 1/2-inch for shallow boxes and 8-32 x 3/4-inch for deeper ones to get a good bite.

The slots are cut cleanly and didn’t snag the screw heads. I tested with both pan head and truss head screws; both seated well and kept the plate from walking when tightened.

Fit and compatibility

This is a true 4-inch square cover sized for standard 4-inch metal junction boxes. It sits flat against the box and doesn’t have a raised “device” profile, so don’t expect to mount a switch or receptacle directly to it. If you need a device, you’ll want a raised cover or a mud ring.

Across a handful of boxes (Raco, Crouse-Hinds, and a generic no-name), the fit was consistent. Hole spacing matched, and the cover covered—no pun intended—the box edges fully, even on a box that had seen a lot of drywall knife abuse. If your box sits recessed more than code allows, this won’t magically fix that; you’ll still need a box extender. But for flush or near-flush boxes, it finishes cleanly.

The 1/2-inch knockout in the center popped out predictably with a flat screwdriver and a twist. The edge of the knockout is moderately sharp, as most are; if you’re running flexible cord with a strain relief, you’ll be relying on the bushing of the fitting, not the raw steel edge. For EMT or flex conduit, I used standard 1/2-inch fittings and had no trouble getting them to seat.

About that 1/2-inch knockout

A center knockout on a blank cover is a thoughtful touch. I used it three ways:

• As a pass-through with a cord grip to feed a temporary tool circuit in a shop while still keeping the junction enclosed and protected.
• With a 1/2-inch flex connector to add a short whip to a new junction without reworking the box entries.
• As a mount for a lampholder stem during a repair, before swapping to a proper fixture.

One caution: not every situation is appropriate for using the cover as your conduit entry point. The cover is removable, so make sure your installation remains secure and compliant when the cover is off (for inspection, for example). In most cases, that means keeping conductors and splices supported within the box and using proper fittings with bushings. If you’re unsure, check local code or stick to entries through the box knockouts.

Safety and finish details

As a flat blank, this is essentially a safety lid: it closes a live junction, prevents accidental contact, and keeps the interior reasonably protected from dust. It is not gasketed or weatherproof. I wouldn’t use it outdoors or in washdown spaces unless it’s inside a listed enclosure that provides the environmental protection.

Bonding is as expected: the steel cover bonds to the metal box via the screws. That’s typical and all you need for a blank cover; there’s no separate ground screw on the plate, nor should there be.

The corners are slightly radiused, which helps avoid snagging, and the edges didn’t burr under screw pressure. I pushed a screwdriver along the edge to test for flaking; the galvanization held.

What I like

• Sturdy galvanized steel that resists flexing and keeps its shape
• Angled keyhole slots that genuinely speed up installation and fix mild misalignments
• True-to-size 4-inch cover that fits a range of common metal boxes
• Useful center 1/2-inch knockout for fittings or cord grips
• Paintable finish that can be made to disappear in finished spaces
• Sold as a four-pack, which is a practical quantity for punch list work

What could be better

• No screws included. Not a dealbreaker (most boxes have them), but having a few 8-32s in the bag would save a trip.
• The knockout edge is typical sharp; plan to use quality fittings with bushings. I’d love to see a slightly chamfered knockout on future runs, though that’s rare in this category.
• Not for outdoor use as-is. A gasketed option would be interesting for damp locations, but that’s really a different product.

Durability over a few weeks

I installed one in a high-traffic garage where it’s likely to get bumped. After a few weeks, no dents, no rust bloom, and no loosening. The others in a basement utility room and a workshop ceiling look the same as day one. This is the kind of part that should be forgettable—in a good way—and so far it is.

Practical tips

• Keep a mix of 8-32 machine screws in your kit (1/2, 5/8, and 3/4 inch). It makes mounting easier, especially on deeper boxes.
• If painting, degrease, scuff lightly, prime, and finish with a durable enamel. Remove the knockout after painting to keep the edge coated.
• For conduit or cord entries through the center KO, always use a listed fitting with a bushing or strain relief. Don’t run conductors through the raw knockout hole.

The bottom line

The KK magsun square box cover does the simple job it’s designed for—and does it well. The angled mounting slots make a real difference in the field, the steel is sufficiently robust, and the center knockout adds flexibility without complicating the design. I appreciate that the covers arrive flat, clean, and ready to use. There’s nothing fussy here, and that’s exactly what I want from a blank cover.

Recommendation: I recommend this cover for anyone who regularly finishes or services metal 4-inch junction boxes—electricians, facility techs, and DIYers with a few projects around the shop or garage. It’s a straightforward, durable, and time-saving plate. Just toss a handful of 8-32 screws in your bag, and you’ll be set.