Brad nails: length, glue and where they belong

A brad is a thin nail, usually 18 gauge, driven by a pneumatic or battery nailer. The wire is about 1 mm thick and the head is barely wider, so the hole it leaves is small enough to fill and forget. That makes brads the fastener of choice for trim, mouldings, cabinet backs and drawer bottoms, and for holding parts in place while glue cures. What they do not do is hold much on their own.

What a brad is for

A brad’s job in furniture is usually to replace clamps. Glue a moulding to a case, pin it with a few brads, and you can move on while the glue sets; the brads keep the part from sliding on the wet glue and hold it tight to the surface. Once the glue has cured, the glue is the joint.

On its own, a brad has little holding power. The shank is thin and smooth, so it pulls out far more easily than a screw. Brads alone are fine for parts that carry no load: a plywood back that sits in a rabbet, a bead of trim, a dust panel. They are the wrong choice for anything that is pulled, racked or hung from, such as a shelf support, a face frame on a heavy door, or a chair.

Choosing a length

18-gauge brads are commonly sold from 5/8” to 2” long. Length is set by two numbers: how thick the piece you are nailing through is, and how much brad you need in the piece behind it.

• Glued joints. The brad only has to hold until the glue cures. About 1/2” into the receiving part is plenty.
• Unglued joints. The brad is the joint, so it needs more grip. A common rule is to have about twice the thickness of the top piece in the part below, which is the same as a nail about three times the thickness of the piece being fastened.

A nailer sets the head a little below the surface, typically about 1/32”, so the tip ends up that much deeper than the brad’s length suggests. Account for it when the receiving part is thin: a 1” brad through a 1/4” back into a 3/4” side reaches 1-1/32” and comes out the far side by 1/32”. A 3/4” brad is the right length there.

Measure your actual stock. “3/4-inch” plywood is often 23/32”; see nominal and actual sizes.

Driving brads without trouble

• Keep your hand off the far side. A brad that meets hard grain or a knot can turn and come out of a face, sometimes a long way from where it went in. Hold the part away from where the brad will travel.
• Square to the surface. Hold the nose of the nailer flat on the work. A tilted nailer drives at an angle and is more likely to exit a face.
• Mind the grain. An 18-gauge brad’s cross-section is slightly rectangular. Holding the nailer so the long side of the head runs with the grain reduces splitting in thin or hard stock.
• Stay back from ends. In hardwood, a brad close to the end of a board can split it. Keep about 1/2” back where you can, and test on scrap of the same species.
• Angle pairs for more grip. Two brads driven at opposing angles lock a part on better than two straight ones.
• Set the depth on scrap. Adjust the nailer so heads sink just below the surface. Too deep crushes the fibres around the hole; too shallow leaves a head to catch a plane or sander.

Without a nailer, brads can be driven with a light hammer and sunk with a nail set. In hardwood, drill a pilot first: chucking a brad itself in the drill makes a hole the right size.

Filling the holes

Fill brad holes with wood filler or putty matched to the finished colour. Filler under a stain often shows lighter than the wood around it, so many woodworkers apply the finish first and fill with a coloured wax or putty afterwards. Test on scrap with the finish you will use.

Brads and wood movement

Plywood, MDF and thin mouldings move very little, so brads around them cause no trouble. A wide solid-wood part is different: it swells and shrinks across its grain with the seasons, and a rigid fastening across that width can make it crack (see wood movement).

Brads are thin enough to flex a little, which is why a common approach to a moulding running across the grain of a solid case side is to glue only the front few inches and pin the rest with brads. Do not rely on brads to let a wide solid top or panel move; use one of the methods in attaching a solid-wood top.

Brads, pins and finish nails

18-gauge brads sit between two other common nailer fasteners:

• 23-gauge pins are thinner still, often headless, and leave an almost invisible hole. They hold very little and are used for small trim and for holding glue-ups.
• 16-gauge finish nails are thicker, with a larger head and more holding power, for face frames and heavier trim. They leave a bigger hole.

For pinning mitred trim, see also mitre joints.

In GrainDraft

Brad nails are one of GrainDraft’s nine joint families, as 18-gauge brads. You choose two parts, then set the brad length, how many, and whether the joint is glued; glued is the default. GrainDraft suggests a length that reaches into the second part without breaking through, counting the 1/32” the nailer sets the head. It warns when a brad would come out the far side, when it reaches too little into the receiving part, and when unglued brads are the only thing holding a part. Brads appear on the shopping list and in the glue-up steps of the build guide; nothing is drilled, so they never appear as a cut.

Related: pocket holes, mitre joints.