Pocket-hole screw

Overview

Pocket-hole joinery drills a hole at an angle, usually 15 degrees, into one workpiece and joins it to another with a self-tapping screw. The screws used are pocket screws: self-tapping with a wide washer head that spreads the load and prevents the screw going too far into the joint. They are the way to join a face frame, add a table rail to a leg, fix a cleat or a plinth, or build quick plywood carcases without clamps.

Types and sizes

• Thread: coarse for softer wood and sheet goods; fine for harder wood.
• Length depends on the thickness of the two pieces, an important layout factor: 25 mm (1 in) for 12 mm (1/2 in) stock, 32 mm (1-1/4 in) for 19 mm (3/4 in), 38 mm (1-1/2 in) for 25 mm (1 in), 50 mm (2 in) for 30 mm (1-1/4 in) and thicker.
• Head: flat washer head; maybe square or Torx drive.
• Finishes: zinc-plated for indoors, stainless for outdoors, or coated screws that resist staining.

Where it is used

Pocket screws appear in contemporary carcase work, cleats and plinths, and quick prototypes. The example library's blanket chest and wall shelf use joinery pocket_hole for hidden fixings, such as plinth cleats screwed up into the carcase. They are not a period fastener; no style guide lists them, so the styles list is empty.

Choosing and sizing

Match the screw length to the board: the screw must stay inside the second piece, with at least 12 mm (1/2 in) of thread in it. Space pockets 75 to 150 mm (3 to 6 in) apart along a joint, and 25 to 38 mm (1 to 1-1/2 in) from each end. A tabletop wants two to three screws per rail; a plinth cleat needs one every 100 mm (4 in).

Installation

1. Clamp the board in the jig with the face you want hidden facing the jig, set the depth stop to the stock thickness, and drill the stepped pocket.
2. Hold the second piece square and flush; clamp it with a face clamp.
3. Drive the screw until the head seats in the pocket, stop at once; the washer head should sit just below the pocket's flat.
4. Add glue only for long-grain to long-grain; end-grain joints do not hold glue.

Wood movement and species

A rigid pocket screw across a wide board will crack it as the board changes width. Use pocket screws along the grain direction, not across. Screws in the end grain of softwood hold poorly; place the pocket in the face or edge, as the sources advise. In MDF (medium-density fibreboard) and Particleboard edges the hole can blow out; use a coarse thread or a Confirmat screw.

Common mistakes

• Screw too long, so it pokes through the second board's face.
• Pockets on the visible side; plan the hidden face.
• Over-driving, which strips the wood around the head.
• Joint creep, because the pieces were not clamped as the screw pulled.

Related

• Wood screw: the ordinary alternative, visible.
• Confirmat screw: the sheet goods equivalent.
• Z-clip, Figure-8 tabletop fastener: ways to attach a top.