Minimum Wall Thickness for Screws

Hollow Walls

• Drywall is usually the thinnest type of wall used in homes. It can as little as 1/2-inch thick. In most cases, however, you don't have to worry about a long screw protruding through this thin wall and out the other side, because the wall is hollow in the middle. The screw will protrude into the space behind the drywall that houses the electrical wires and plumbing. More important is the weight-bearing ability of the screw. Drywall is not strong enough to hold heavy objects such as large mirrors. If you are using a screw to hang something heavy on drywall, your best bet is to use a toggle bolt or anchor, which is a Phillips-head screw and nylon or metal anchor. Insert the screw into the anchor, which has "wings" that open behind the drywall to securely hold the screw -- and heavy object -- in place.

Solid Walls

• Solid walls don't allow for the use of anchors, so if you have a thin but solid wall, carefully choose the size of your screw. Choose one that is shorter than the thickness of the wall -- screw lengths are measured in inches -- and has a tapered point. These are called self-threading screws because they fasten as you turn them. In addition, choose one that has threads that extend all the way up to the head of the screw, so the screw can lie flush against the wall.

Concrete or Masonry Walls

• Concrete or masonry walls are rarely thin, but they still require a special screw. Masonry wall screws are made with alternating, diamond-cut threads in order to be able to penetrate the hard surfaces of brick and concrete. These screws are often marketed as for use in concrete only, so they are easy to identify at hardware stores. Some come with anchors for bearing very heavy loads.

Other Considerations

• Screws that have fine threads are stronger than those that have wide-set or course threads, so choose these if you are hanging something heavy on the wall. In addition, always allow for the thickness of the items you are attaching to the wall. The screw should be long enough to penetrate the item and a good portion of the wall behind it. Otherwise, the item may not be securely attached to the wall.