The most secure way to attach anything to a wall is to nail or screw it to a stud, but studs aren't always located just where you need them. When a stud isn't available, wall anchors are, but it's important to use the right one. There are several varieties, and they are rated for the amount of weight they can hold. Moreover, some are more suitable for masonry and concrete walls than for drywall.
Types of Anchors
Every hardware store carries an assortment of wall anchors that can be grouped into three broad categories. In the first are plastic and metal cones that wedge into a pre-drilled hole, and in the second are anchors that you screw directly into the wall. The third category includes two-piece anchors with a sleeve and a machine screw that hook against the back of the wall covering. Anchors in the third category, which includes toggle bolts and molly bolts, are capable of supporting more weight than other types of anchors, but they aren't necessarily the best choice for every job.
When selecting a wall anchor, it's prudent to plan ahead to the time when the anchor no longer serves a purpose and must be removed. Anchors capable of supporting heavier weights do so by becoming a virtually permanent part of the wall, and removing one often means cutting a a hole around it and pushing it behind the wall. Conical and screw-in anchors, on the other hand, are relatively easy to remove and leave a small hole that you can patch with joint compound or another type of filler. They are best when affixing lightweight objects that you may move.
The facility with which you can remove conical anchors is the main reason why you shouldn't rely on them to support more than 10 pounds in drywall. A strong outward force or an impact to the object they're holding can dislodge them. Toggle bolts, on the other hand, won't dislodge unless the drywall breaks, and the strongest ones can hold 50 pounds or more. The relative strengths of molly bolts, plastic wing anchors and screw-in anchors are between these extremes. When affixing a moderate weight, your choice may come down ease of installation. If so, you may choose a screw-in anchor or self-tapping molly bolt.
Your choice of anchor may be determined by wall material as well as by the object you are attaching. Conical anchors can hold more weight in a concrete, masonry or tile wall than in one covered with drywall — and may be the only kind of anchors that will work. Drywall and plaster walls, on the other hand, are relatively thin and easy to penetrate, so almost any anchor will work. When choosing an anchor, always err on the side of stability by choosing one that will support more weight than you plan to put on it.