The Nuts and Bolts of Picking the Right Fastener Where Nails Won’t Hold

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 onto 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 also are 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. For demanding structural uses, discuss the problem with your dealer.

Here are a couple of 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 not only draws the connected member toward the concrete, but the taper at the end drives the steel band outward to grip the hole.

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. Available in sizes ranging from three-sixteenths to 1 1/4 inches in diameter, this fastener is rated by the manufacturer with up to a 4,000-pound working load, depending on size and the base material.

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-quarter-inch diameters, this fastener has an expanding body that contains a steel driving pin. After being inserted into a hole, the pin is driven flush with the anchor to grip the base material.

A nylon anchor, similar to the nail anchor, has a nylon body that increases its versatility. In addition to concrete, it is appropriate for masonry applications and it even handles hollow wall fastening. Its head has a screwdriver slot, and the top of the pin is threaded so it can be withdrawn to remove the fastener.

A hollow set drop-in, similar in principle to the expansion anchor, is designed for light- to medium-duty use in the relatively thin walls of hollow concrete block. It is made up of a tubular, split body and a lower internally threaded cone. A bolt threaded into the cone expands the body against the hole. The hollow set drop-in is available in sizes from one-quarter to five-eighths of an inch.