You already know how to cut a mortise-and-tenon. Posts 67 through 70 covered that. The bridle joint is the same geometry with one wall missing. The mortise becomes a slot, open at the end grain. The tenon slides in from above. And when the joint closes, everything is visible. Both end-grain faces, both cheek surfaces, the shoulder line. Nothing hides.
That visibility changes three things: how you cut, how you fit, and where you look when something's wrong.
Where you'll use it
Frame corners. Two rails meeting at a corner of a table base, a trestle, a sawhorse. The bridle connects them faster than a closed mortise-and-tenon, with more glue surface than a dowel, and without the fuss of chopping to a blind floor. The open end usually gets covered by a leg or another component anyway.
T-intersections. A rail entering the middle of a leg. The end grain shows at the face of the leg, which means you're making a design decision whether you meant to or not.
Chairs and benches. Seat rails to front legs, stretchers to legs. The bridle tolerates racking forces better than a dowel. Long-grain to long-grain glue holds when the chair gets shoved back from the table for the thousandth time.
Sawhorses and workbench trestles. Speed matters here. Mark, saw, done. No chopping to depth in a blind cavity.
Layout
One rule runs the whole layout: gauge from the same face for both pieces, and do it before you touch a saw.
Set a marking gauge to one-third the stock thickness. That's the cheek offset. Same proportion as the dado depth rule, for the same reason. More than a third weakens the slot side. Less than a third makes a tongue too thin to glue reliably.
Mark the slot width on the end grain of the slot piece. Gauge lines from both faces. The gap between them is the slot. Both lines from the same setting, not two independent measurements, so both cheeks stay symmetrical.
Mark the tongue on the rail with the same gauge setting. Then mark shoulder depth from the actual slot floor measurement. Set the gauge to your widest chisel (R488), check it once on a test piece, and run it on every part before you pick up a saw.
Cutting the slot
Two walls and a floor. Saw both cheeks first, rip cuts, saw in the waste. Both cuts from the same end. If you saw them separately from opposite ends, you introduce a twist. The slot walls need to be parallel.
Remove the waste between the cheeks. A coping saw for narrow slots, a chisel for wide ones. The floor needs to be flat. A router plane is not always necessary here, but it's always correct when flatness matters.
The open end is the advantage. You can see the floor, check it with a straightedge, pare directly. No working blind. The slot is honest about its own accuracy.
Cutting the tongue
Two shoulders, not four. That's what separates this from the full tenon.
Mark shoulder locations from the slot floor depth. Knife the line. Saw the shoulders using the bench hook procedure from Post 67. The cheeks are rip cuts from the shoulder to the end of the rail.
End grain shows at the tip of the tongue. Plane it flush after fitting if you're leaving it exposed. A shoulder plane or a card scraper brings it to the same surface plane as the slot walls.
Fitting
This is the most direct fit test in the whole arc. Slide the tongue into the slot by hand. You can see every surface. You can see exactly which cheek is binding and which is loose. Chalk transfer still works if you need it, but most of the time you won't. The fit tells you visually what the dovetail required diagnostic chemistry to reveal.
Same standard as every joint in this arc: closes under hand pressure. Not a rattle, not a force fit. Shoulders seat against the slot floor with no gap and no resistance.
One check worth building into habit: sit the assembled corner on a flat surface and sight across the shoulders. If one is proud, you have a twist in the slot floor. Router plane, one light pass.
How it holds
Strong in compression and shear. The long-grain glue surfaces are substantial and parallel to the load. Weak in tension. Without a peg, pulling the joint apart along the rail can fail the glue.
In most furniture, tension isn't the loading condition. Frames are compressed by weight. But if it is the condition (a trestle under eccentric load, a door frame with a heavy panel), bore through both cheeks and drive a drawbored peg. Now it holds in every direction.
Three failure modes
The shoulders don't close. The tongue is too long. It bottoms out in the slot before the shoulders reach the floor. Fix: pare the end of the tongue, not the shoulders. Fit the shoulder, not the face.
The joint racks corner to corner. The slot cheeks and tongue cheeks aren't parallel. One rip cut drifted. Chalk the high cheek, pare it flat, check with a straightedge before re-assembly.
The open end shows a gap. A wedge of daylight where the tongue enters means the slot is narrower at the entry than at the floor. Saw drift during the cheek cuts. Pare the tight end of the slot walls back to parallel. You can catch this before fitting if you sight down the slot first. Good habit to build.
The closed mortise-and-tenon hides its geometry. The bridle shows it. Same surfaces, same tools, same layout principles. What changed is only what's exposed. That's not cosmetic. That's a choice about where the evidence of making lives.