A dovetail locks itself together. Pull it apart without glue and the angles fight you. That's the whole point of a dovetail. It was designed for the tension loading of a drawer being yanked open ten thousand times.
A box joint doesn't do that. Pull the fingers apart without glue and they slide right out. No resistance. No geometry working in your favor. The box joint is a glue joint, full stop. What it gives you is surface area. Cut eight fingers on each board and you've got sixteen long-grain glue walls. In decent wood with decent glue, the wood beside the joint fails before the joint does.
Same applications as the dovetail: drawer corners, box corners, tool trays, small casework. Different argument entirely.
What it is
Interlocking rectangular fingers at the corners of two boards. Every finger on one board fits a matching socket on the other. Unlike dovetails, where each mating pair is unique, box joint boards are interchangeable. Cut a whole run to the same jig setting and any board mates with any other board. The dovetail is a direct-transfer joint. The box joint is a template joint. It scales.
The arithmetic problem
All fingers must be equal width. That's the governing rule, and it creates a planning problem you solve before the first cut.
A 6-inch board with 3/4-inch fingers gives you exactly eight fingers. Clean. No problem.
A 5-1/2-inch board with 3/4-inch fingers gives you 7.33 fingers. That doesn't work. Your options: change the finger width until the division comes out clean, design the board width around the finger width, or accept a half-width finger at each edge. Half-width edge fingers are common and structurally fine.
This is a decision you make at the design stage. Discovering the arithmetic problem when you're standing at the saw is a layout failure.
The jig
The box joint jig is one of the few places in furniture making where a dedicated jig is the right call. Not because hand layout is impossible, but because the spacing accuracy required across eight or twelve fingers compounds with each cut.
The standard version is simple. A fence rides the table saw miter slot with a hardwood pin projecting from it. The pin width equals the finger width. The pin sits one pin-width from the blade. Place the board against the fence with one edge against the pin, cut the first notch. Lift, set the first notch over the pin, cut the second. The pin is self-spacing.
Dial it in on scrap first. Always. A correct box joint fits with hand pressure. Snug, no gaps, no force. If the fingers are too tight, the pin is slightly too close to the blade. If they rattle, it's too far. A half-turn on the adjustment moves you from tight to loose faster than you'd expect. Cut test joints until the fit is right, then cut your parts.
The hand-tool version
For a single box or a pair of drawers, the jig is often more trouble than it's worth. Mark out the fingers on one board with a marking gauge and combination square. Same equal-width spacing, same decision about edge fingers. Every line gets the knife.
Cut the cheeks with a pull saw, waste side of the line. Clear the waste with a coping saw and pare the floor flat with a chisel. Transfer to the mating board directly: hold the first board against the second, register the baseline, mark through the sockets. No measurement. Direct transfer. Fit the same way as everything else in this arc: hand pressure, chalk transfer, pare only what's marked.
Where the strength actually lives
Here's the part people get wrong. They look at a box joint and think the glue bond is at the finger tips, where end grain meets end grain. That's the part you see when you look at the corner. But end grain to end grain is one of the weakest glue surfaces in woodworking. The cells are open tubes running perpendicular to the glue line. The adhesive gets pulled into the fibers instead of forming a bond between surfaces.
The real glue surface is the long-grain walls of each finger. The sides, not the tips. When you assemble a box joint, each finger is surrounded on two sides by long-grain walls of the mating board. More fingers means more of these walls. A narrower finger pitch on thicker stock is stronger than wider fingers because the surface area grows faster than the joint count.
This is why box joints need real clamping pressure. The long-grain walls need full contact before the glue sets.
Assembly
Box joints go together all at once. All fingers entering all sockets simultaneously. That makes them more demanding to assemble than a standard mortise-and-tenon. A dry run is not optional.
Glue all long-grain walls. End grain tips get glue too, for insurance, but they're not doing the work. Apply clamp pressure parallel to the fingers, not across the corner. Use a caul the full width of the joint to distribute pressure across all fingers at once.
Check diagonals at assembly. A box that closes but isn't square will be square when the glue sets, and there's no correcting it after.
Three failure modes
Fingers won't close. The jig pin was set too close to the blade, or a hand-cut joint was cut slightly proud of the line. Chalk one mating surface, assemble as far as it goes, part carefully, pare only what's marked. Never force a box joint together. You'll split the short grain between fingers.
Gap at the socket floor. The finger is shorter than the socket is deep. Usually because stock thickness wasn't confirmed before setting the jig, or because a hand-cut floor wasn't chiseled to full depth. The gap shows at the inside corner. Only fix is a deeper cut or a chisel pass to full depth.
Visible step at the corner from unequal finger widths. This is a layout error, not a cutting error. If the jig pin was set up on stock of different thickness than the final parts, the finger-to-socket ratio is off. Test joints from the same stock as your parts.
The box joint doesn't have the mythology of the dovetail. Nobody puts one on the cover of a magazine. But it holds the wood, it does it predictably, and if you can do arithmetic and set a jig, you can cut a hundred of them to the same spec before lunch.