Of all the different types of drywall anchors, conical plastic ones are the most lightweight. They are great for hanging pictures, attaching towel racks to the wall and even hanging small shelves, but you shouldn't rely on them for hanging cabinets or heavy items, such as a large mirror, from drywall. The problem is the crumbly nature of drywall. When you put enough lateral pressure on a ribbed anchor, it pulls the drywall out with it.
Ribbed plastic anchors work much better in hard materials, such as masonry, brick and ceramic. They expand when you drive the screw and hold it securely, provided that the pilot hole is the right size. In fact, failing to size the hole correctly is the only way you can make a mistake when installing a conical screw anchor.
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Drywall Anchors Weight Limit
Conical anchors are one of a number of types of drywall anchors. Tests show they can handle about 80 pounds of downward pressure before they pull out of standard 1/2-inch drywall. Threaded plastic anchors can handle 110 pounds, and threaded brass ones stay in place under a maximum load of 130 pounds. Molly bolts, which consist of an expandable metal sleeve and a metal machine bolt, can hold 170 pounds.
Toggle bolts, which also consist of a bolt that screws into a sleeve, are the strongest drywall anchors.. The sleeve has wings that expand and anchor to the back of the drywall. A toggle bolt can support upward of 300 pounds. It's limited by the strength of the drywall itself, which will probably break before the bolt fails.
Note that all of these weight limits apply to situations where the hanging item is pulling straight down on the anchor, perpendicular to the anchor's length. By contrast, if the force is pulling straight out on the anchor, such as with an item hung on the ceiling, most anchors have greatly reduced holding power; this is most true with cone-shaped ribbed anchors.
How to Install a Ribbed Anchor in Drywall
When you buy conical plastic wall anchors, the package usually identifies the size of the drill bit you need for the pilot hole. If not, measure the outside diameter of the shank of the anchor about halfway between the screw opening and the tapered end, and use a drill bit with that diameter. The goal is to drill a hole into which the anchor will fit as tightly as possible. You don't want to make the hole too small, though, or you won't be able to tap the anchor into place.
After drilling the pilot hole, insert the anchor and tap it with a hammer. Use light pressure to avoid bending the anchor, and keep tapping until the flange around the opening is flush with the wall. If you need to remove an anchor, drive a screw part way and pull on the screw with pliers or a hammer claw. The anchor will come out of the wall with the screw.
Installing a Ribbed Anchor in Concrete or Ceramic
The procedure for installing a plastic screw anchor in a hard material such as concrete, brick or ceramic is the same as for installing one in drywall, but drilling the hole for it is more challenging. Use a masonry bit and set the drill at half speed to avoid overheating. On smooth surfaces such as shower tiles it's a good idea to apply masking tape to the surface before you drill. The tape prevents the drill tip from wandering.
The holding power of plastic wall anchors is much greater in hard materials than it is in drywall, provided that they are tight. You can use them to hang cabinets, shelves and other heavy items on brick and concrete walls.