MATERIALS : Has Gravity Got Your Wall Hangings Down? Fasteners Can Help

Have you ever wondered why a nail works so well in wood? It’s not the nail that’s doing all the work--it’s the wood. Because wood is resilient, it grips the nail, not the other way around.

The trouble is, there are a lot of building materials that are not so cooperative. While hardened spiral nails will stay in concrete, their holding power isn’t that great.

And forget about drywall. Nailing to a wall really means getting out the stud finder to find a 2-by-4 that’s hidden inside.

Fortunately, there’s a wide assortment of fasteners that don’t rely so much on the gripping power of the base material.

These devices provide their own gripping power and are designed to suit specific applications.

There are concrete fasteners that expand to grip the walls of a hole, and myriad hollow wall fasteners that latch on to drywall with a vengeance.

You’ll find most of these fasteners, or close variations, at your hardware store. Bear in mind that each design has specific capacities.

Manufacturers test maximum sustainable loads in terms of tension (a load in line with the fastener axis) and shear (a load perpendicular to the fastener axis).

Loads are also based on the base material and safe working loads are rated at one-fourth the maximum load.

In general, light-duty loads are less than 400 pounds, medium-duty loads range from 400 to 4,000 pounds and heavy-duty loads are above 4,000 pounds. Discuss demanding structural uses with your dealer.

Here are a few examples of the many specialty fasteners available:

An expansion anchor is a concrete fastener that features a carbon-steel band that fits over a reverse taper at the end. The top half is threaded to accept a standard nut.

In use, a hole is bored and the fastener is driven in place. When the nut is tightened, it draws the connected member toward the concrete, and the taper at the end drives the steel band outward to grip the hole.

One model is called a Wedge-Grip anchor and comes in diameters ranging from one-fourth inch to one inch. It handles medium- to heavy-duty loads depending on size. A pack of five one-fourth-by-1 3/4-inch anchors costs about $2. (Star Expansion Co., Pleasant Hill Road, Mountainville, N.Y. 10953.)

A threaded spike is driven into a hole that matches the shank diameter. The bend in this fastener exerts tremendous force against the surrounding wall. It’s available in sizes ranging from three-sixteenths to 1 1/4 inches in diameter. The manufacturer rates this fastener with up to a 4,000-pound working load depending on size and the base material. The one-half-inch-diameter Threaded Spike costs about $1. (The Rawlplug Co. Inc., 200 Petersville Road, New Rochelle, N.Y. 10802.)

A nail anchor is the ticket when it comes to such light-duty tasks as securing junction boxes, conduit or ductwork to concrete or block. Available in three-sixteenths- or one-fourth-inch diameters, this fastener has an expanding body that contains a steel driving pin. After being inserted in a hole, the pin is driven flush with the anchor to grip the base material. One-fourth-inch nail anchors cost about $1.20 for a pack of four. (Star Expansion Co.)