Fasteners hold a joint closed while glue dries, or hold it on their own when glue is not practical. Picking the wrong one leaves a joint that splits, pulls out or does not close. The choices come down to type, gauge, length and pilot hole.
Nails and brads
Finish nails and brads are thin, with a small head that can be set below the surface and filled. Their gauge is a number where a bigger number means a thinner nail.
| Type | Gauge | Use |
|---|---|---|
| 23-gauge pin nail | very thin | Holding a part while glue dries; nearly invisible |
| 18-gauge brad nail | thin | Trim, small boxes, thin parts |
| 16-gauge finish nail | thicker | Trim, casing, stronger holds |
A pneumatic nailer drives them at speed. A nail holds best in shear, sideways across its shank, and poorly in a straight pull, which is why nails suit trim and holding parts flat, and not structural joints. Use nails with glue: the glue does the work and the nail clamps the joint until it cures.
Wood screws
A wood screw has threads that pull the boards together and hold against a pull. Screws are given a gauge number for the shank diameter, such as #6, #8 and #10, and a length. The fasteners database lists the shank diameter for each gauge, and recommended pilot hole sizes for hardwood and softwood.
| Gauge | Shank diameter | Typical use |
|---|---|---|
| #4 | about 0.112 in | Small hardware, hinges on boxes |
| #6 | about 0.138 in | Light assembly, cabinet backs |
| #8 | about 0.164 in | General furniture and shelves |
| #10 | about 0.19 in | Heavy framing, workbenches |
| #12 and #14 | 0.216 and 0.242 in | Structural, timber |
A common rule for length: the screw should go through the first board and reach about two thirds of the way into the second. Through a 3/4 inch board into another 3/4 inch board, a 1-1/4 inch or 1-1/2 inch screw is right.
Pilot holes and countersinks
A pilot hole is a narrow hole drilled ahead of the screw. It removes a column of wood the size of the screw core, so the screw can be driven without forcing the fibres apart. In the top board, drill a clearance hole as wide as the shank, so the screw slides freely and pulls the two boards tight. In the bottom board, drill the pilot a little smaller than the thread root. The database lists the pilot bit size for each gauge in both hardwood and softwood, such as 1/16 inch for a #4 in hardwood and 3/64 inch in softwood. Hardwoods need a pilot that is slightly larger than softwoods.
A countersink is a cone-shaped recess that lets the head sit flush or below the surface. Combination bits drill the pilot, clearance and countersink in one step. For a plug, drill a counterbore deeper than the head and fill it with a wood plug so the screw does not show.
Pocket screws
A pocket hole jig drills a shallow angled hole in the end of a board, with a flat-bottomed counterbore for the head, and a pilot that continues to the edge. The screw runs at about 15 degrees through the first board into the second. Pocket screws have a flat washer head that seats on the bottom of the pocket and a coarse thread for softwood or fine for hardwood.
The lengths are matched to the board thickness.
| Board thickness | Screw length |
|---|---|
| 1/2 in | 1 in |
| 3/4 in | 1-1/4 in |
| 1-1/2 in | 2-1/2 in |
The database lists pocket screws at 1, 1-1/4, 1-1/2 and 2-1/2 inches. Pocket joints are fast, but the board can slide as the screw is driven; clamping the joint while driving keeps the faces flush.
Confirmat screws
A confirmat screw is a thick, coarse-threaded screw for particleboard and plywood carcases. It has a large shank and needs a stepped drill bit. It gives a strong hold in materials where standard screws pull out.
Avoiding splits
- Drill a pilot hole at the right size.
- Keep screws at least half an inch from the end of a board.
- Stagger screws along the grain, so they do not sit in one line.
- Drive slowly in hardwood, and back out a turn when the torque rises.
- Use a wax or soap on the threads in dense woods.
Choosing by material
| Material | Fastener |
|---|---|
| Softwood | Coarse-thread screws, fewer pilot requirements |
| Hardwood | Fine-thread screws, full pilots |
| Plywood | Fine-thread screws or confirmat |
| Particleboard | Confirmat or special screws |
| Trim | 16-gauge or 18-gauge nails |
Plan the count
Use enough fasteners to close the joint evenly. Two screws at each end of a shelf rail are enough for most uses; three to four are needed in a long rail. The cut list packer will tell you how many boards to buy, and a count of joints in the plan gives the number of fasteners.