Nail and Screw Sizing Fact Sheet

The following nail and screw fact sheet will help you pick what size screw and nail to use for fastening jobs. Although there is seemingly nothing complicated about a nail or a screw, many are misused due to improper sizing. Therefore, determining the right nail and screw sizes is essential for the success of your project.

Selecting the Proper Nail and Using it Correctly

Although there are many different types of nails and brads, four types will handle most fastening jobs.

The common nail is most widely used. It has a flat head and is used where the appearance of the nail head is not objectionable. The length of a common nail is identified by its "penny" size. In the early days of nail manufacturing, this term designated the weight of nails per hundred. Today it designates only the length and size of the nail. The designation 2d, 3d, 4d, etc., identifies a 2-penny, 3-penny, 4-penny nail, etc.

The casing nail is used primarily on cabinet work or interior trim. Casing nails are slightly heavier than finish nails. The heads of casing nails are normally countersunk and covered with putty or wood filler to hide them from view.

Finishing nails have rounded heads that can be driven flush with the surface of the wood. Although they are often countersunk like casing nails, they can be used without countersinking.

Common brads are designated by length only. Brads are recommended for light assembly work where the head should be concealed. They are thinner, shorter, and smaller than finish nails.

Use the nail selection chart below for selecting the proper nail or brad for various thicknesses of wood. The chart shows the recommended type and size of nail or brad for woods of various thicknesses. You may want to make some variations from the chart, but it can be a practical guide in nail selection.

Here is a rule of thumb to remember when choosing size: the nail should always be about three times as long as the thickness of the wood through which it is driven. Nails are normally driven through a thin piece of wood and into a thicker one. This allows 2/3 of the nail to provide holding power in the thick piece. To help you pick the right length of nail, hold the nail up against the piece you're putting it through. Then select a nail approximately three times this thickness.

Now that you know about nail types, it's important to know how to use them. The picture below illustrates how to countersink a nail. First, select either a casing or finish nail and drive it into the wood, leaving the nail head slightly above the surface. Select a nail set with a head the same size as the head of the nail and drive the head of the nail slightly below the surface with the nail set. Remove the nail set and fill the recessed area with wood putty or wood filler. Let the putty dry, then sand it flush with the surface of the wood.

You can conceal nails in a piece of wood by taking a wood chisel and digging a slight hole into the wood, in the direction of the grain (A). Drive a finish or casing nail into the hole and replace the chipped-out wood with wood cement. If done properly, this will provide a strong holding power and the nail will be completely hidden.

Bend nails over at the end when attaching two pieces of wood where appearance is not important. Bending the nail over increases the strength of the joint (B).

Use care when driving nails near the end of a plank. Never drive two nails in the same grain of the wood near the end. Always move over to another grain of wood for inserting the second nail (C).

When you must nail an upright piece of wood to a flat surface, toe-nailing with casing or finish nails will do the job. Drive the nails completely in to provide a strong holding power with a neat appearance (D).

A special type of nail is available for wallboard. This type of nail practically eliminates the popping problem you might have with other nails. The rings around the body of the nail give it an extra-strong holding power, and the dish-shaped head can be driven flush with the surface of the wallboard to provide a neat appearance.

Illustrated in the next image are various types of fasteners that are helpful for specific fastening jobs. A special nail is available for holding wood to concrete (A). With a little patience and practice, the concrete nail can be driven into concrete or masonry.

A ring nail provides a strong holding power for special nailing jobs (B). The annular rings around the nail have sharp ridges that lock into the wood, making it practically impossible for the nail to slip.

Ordinary corrugated fasteners are used for fastening corners or where one piece of wood butts against another (C).

Upholstery nails are designed for fastening materials to wood on both flat and curved surfaces (D). They can be used to cover unsightly tacks.

Selecting the Correct Screw and Using it Properly

Below are the six types of common screws. These screws can be divided into two basic types: slot-head screws and Phillips-head screws. Both types of screws are available with flat, round and oval heads.

And the next figure shows how these three different types of common heads look when driven into the wood. The oval-head screw extends above the surface in a slight oval, the round-head screw protrudes above the surface in a half-circle, and the flat-head screw is flush with the surface.

Use this screw selection chart for selecting the correct size and length of screw for any job. This chart is designed for flat-head screws but can be used for any type. The column on the right shows the size of the pilot hole to be drilled for starting the screw. The chart also gives the relative size of the head and shank of screw sizes ranging from #2 to #16. This will help you select the proper size screw quickly and easily.