Plate sizes and what the adhesive actually holds

Measure the plate you already have

Faceplates come in three common sizes, and the gap between the smallest and the largest is about an inch. That is little enough to ignore and more than enough to matter when one piece has to cover another.

Measure the plate itself rather than the opening in it, and measure both directions. Oversize plates are usually there for a reason: a patch in the drywall, a rough cutout, or paint that stops short of the edges. A cover smaller than the plate underneath will put that reason on display around its border.

One gang, two gang, and a switch next door

A single outlet on its own plate is one gang. An outlet sharing a plate with a light switch is two gang, and the cover for it is wider.

Those wider pieces are handed, and that catches people out. The cutout has to clear the switch, and once the cord channel is in the picture a switch on the left is not the mirror image of a switch on the right. Stand in front of the wall and note which side the switch is on before choosing.

Where the clips hold

The adhesive is made for flat, clean, fully cured surfaces, and on those it holds for years.

• Painted drywall that has been dry for a month or more.
• Smooth painted or sealed wood trim and baseboard.
• Glazed tile and sealed smooth stone, wiped down first.
• Painted metal, such as a door frame.

Where they do not

On these the clip holds for a while and then lets go, usually taking something with it.

• Textured plaster and sprayed finishes. Orange peel, knockdown and popcorn leave the adhesive almost nothing flat to sit against.
• Wallpaper and vinyl wall covering. The adhesive holds fine, and then the paper leaves the wall along with it.
• Paint younger than about thirty days, which is still hardening and lifts in one sheet.
• Whitewash, limewash and chalk finishes, which powder under any tape at all.
• Bare brick, block and unsealed masonry.
• Anything dusty, waxed or greasy. A kitchen wall wants washing and drying before a clip goes near it.

Putting them on and taking them off

Wipe the spot with rubbing alcohol and let it dry. Press each clip hard for half a minute so the adhesive wets the surface rather than merely touching it, then leave the run alone for an hour before letting the cord hang on it. Cold walls hold worse than warm ones, so a room at ordinary temperature is the place to do this.

To take one off, pull the tab slowly along the wall rather than straight out from it, so the adhesive stretches and releases instead of tearing paint away. Warming it for a few seconds first helps. On old or thin paint, go slower than feels necessary.