Finger joint (box joint)
A box joint, often called a finger joint, joins two boards at a corner with interlocking square fingers. Unlike a dovetail, the fingers are straight, so the joint is quick to cut with a jig and gives a large area of side grain to glue. It is the usual corner for boxes, drawers and trays made by machine.
Even spacing
The joint looks best when the fingers come out even across the board. Divide the board’s width by the finger width: a whole number means an exact fit. An odd count puts a finger at both edges of one board and a notch at both edges of its mate, so the corner looks the same either way up; with an even count one edge ends in a finger and the other in a notch.
How it’s cut
On the table saw a dado stack and a jig with an indexing pin cut one finger at a time: each cut is moved over onto the pin to space the next. On a router table a straight bit and a similar jig do the same. Both boards are cut on the same jig, the second shifted by one finger, so they interlock.
Not the structural finger joint
The same name is used for long, tapered fingers that join boards end to end in lumber mills. The Wood Handbook says those end-to-end joints need a glue area at least ten times the board’s cross-section, with a slope of 1 in 12 or flatter for the highest strength. A box joint is a different corner joint and those figures don’t apply to it.
One source: USDA Forest Products Laboratory, the authority for wood adhesive joints it tested
Related joints
Sources
- USDA Forest Products Laboratory, Wood Handbook (FPL-GTR-282, 2021), ch. 10 "Wood Adhesives", End-Grain and End-to-Edge-Grain Joints, read 2026-11-07
Proportions marked as a traditional rule are shop tradition, not measurements. This site gives no joint-strength numbers: the published tests each used a different rig. How we source these numbers.