Pocket holes: screw length, thread type and limits

A pocket-hole joint is a screw driven at a shallow angle through the edge of one board into another. A stepped drill bit and a jig make the angled hole and a flat-bottomed pocket for the screw head. It is fast, needs no clamps once driven, and hides on the back or underside of a piece. Most failures come from mismatched settings, so it is worth getting them right.

How it works

The jig guides a stepped bit at a shallow angle, about 15 degrees on the widely used Kreg jigs, so the screw exits near the middle of the board’s edge or end and bites into the mating part. The screw’s washer head bears on the flat bottom of the pocket and pulls the joint tight.

Two settings must match the thickness of the board you are drilling:

• Jig setting. Moves the guide so the hole exits at the right place.
• Drill collar. Sets how deep the stepped bit goes, and so where the pocket bottom sits.

Use the actual thickness. “3/4-inch” plywood is often 23/32 inch; see nominal and actual sizes.

Screw length

Screw length is chosen from the thickness of the board being drilled. Kreg’s chart gives these for the most common thicknesses:

Material thickness	Screw length
1/2”	1”
3/4”	1-1/4”
1-1/2”	2-1/2”

For other thicknesses, and when joining boards of different thicknesses, use the jig maker’s chart. A screw that is too long can break through the face of the mating board; one that is too short has little thread in the mating part.

Coarse or fine thread

• Coarse thread for softwoods, plywood, MDF and particleboard. The deep threads grip soft or fibrous material.
• Fine thread for hardwoods such as oak, maple and cherry, where coarse threads are more likely to split the wood.

Pocket screws have self-tapping tips and flat washer heads; ordinary wood screws with tapered heads can split the pocket.

Driving and clamping

• Clamp across the joint. Driving a screw at an angle pushes the parts out of alignment. A face clamp holding the two surfaces flush prevents the offset.
• Glue or not. Glue on long-grain surfaces, such as a face frame rail and stile, adds strength and the screws act as clamps while it dries. End-grain joints rely mostly on the screws.
• Drive to snug. Set the drill’s clutch low, especially in softwoods and MDF, so the screw does not strip its hole.

Layout

• Keep holes back from the ends of a joint, about an inch or so, so the screw has wood around it.
• Space holes every 6 to 8 inches along long joints.
• Put pockets on faces that will not be seen: inside a cabinet, under a shelf, behind a face frame. Plugs are available for pockets that do show.

Where not to use pocket holes

• Across the grain of wide solid wood. A pocket screw fixes the parts rigidly. On a wide solid panel or top, it stops the wood from moving and it can crack. Use a method that allows movement, as described in attaching a solid-wood top.
• In very thin stock. Below about 1/2 inch there is little wood for the pocket and the screw.
• Where the joint carries heavy racking loads, such as a chair. A mortise and tenon is far better; see sizing a mortise and tenon.
• Where the pockets would be visible and plugs would look out of place.

In GrainDraft

Pocket hole is one of GrainDraft’s eight joint families. You place an angled screw connection between two parts and review its engagement, edge clearance and the jig settings for your stock in the joint preview. Model parts at their measured thickness so those settings match the board you will drill.

Related: half-lap joints, cut-list planning.