What are tee nuts and cross dowels, and which way round do they go?
The two fittings that put a nut inside a piece of timber — how each carries load, and the orientation error that makes a tee nut pull straight out.
- Difficulty
- beginner
- Time
- 12 min
- Read
- 3 min
Short answer
A tee nut is a flanged collar with prongs, pushed in from the back so that tightening the bolt pulls it further into its seat — which is why it must go on the opposite side to the load. A cross dowel is a barrel with a threaded hole through its side, dropped into a hole bored across the grain so the bolt pulls against long grain instead of weak end grain.
Both of these turn up constantly in flat-pack furniture, beds, climbing frames and workshop fixtures, and both are frequently fitted the wrong way round by people repairing them. The orientation is not arbitrary — it is the whole mechanism.
Step by step
- Identify a tee nut.A steel collar with an internal thread, a wide flat flange at one end, and three or four sharp prongs pointing away from the flange. It looks like a top hat with claws.
- Fit a tee nut from the side away from the load.The bolt has to pull the tee nut into its seat, not out of it. If you fit it on the same side as the load, the flange is pulling against nothing and the prongs alone are holding — and they will let go.
- Drill a plain hole for the tee nut's barrel and seat the flange flush.The hole takes the barrel, not the prongs. Pull the tee nut in squarely with a bolt, a washer and a nut, or tap it home with a block over the flange. Do not hammer it directly — the prongs bend.
- Counterbore in thin material.If the flange would sit proud, cut a shallow recess so it sits flush. A proud flange holds the two pieces apart.
- Identify a cross dowel.A short steel cylinder with a threaded hole through its side and a slot or hex socket in one end so you can rotate it to line the thread up. Also called a barrel nut or a dowel nut.
- Use a cross dowel where the bolt runs into end grain.This is the case it exists for. Bore a hole across the grain for the barrel, intersecting the bolt hole that runs in from the end, then align the barrel's thread with a screwdriver in its slot.
- Understand why the cross dowel is strong.The barrel bears across a wide area of long grain rather than pulling on the end grain, which has very little strength. That is why beds and knock-down furniture use them for the joints that get tightened repeatedly.
- Get the two holes to intersect properly.This is the whole difficulty of a cross dowel. The bolt hole and the barrel hole have to meet, so mark both accurately from the same reference face and drill the barrel hole square.
- Keep the bolts.Cross dowels and tee nuts use ordinary metric bolts, and a replacement is easy to find once you know the size. Measure the thread rather than guessing.
Tips
- If a tee nut keeps pulling out of a chair or a bed, check which side it is on before buying a bigger one. Reversed orientation is the usual cause.
- A tee nut with the prongs bent over during fitting will spin the first time the bolt is loosened. Pull them in square with a bolt and washer rather than a hammer.
- Where a tee nut has already torn out of chipboard, a threaded insert with epoxy in a slightly larger hole is a stronger repair than another tee nut.
Common mistakes
- Fitting a tee nut on the same face as the bolt head — Tightening then pulls it out of its own hole. The prongs are only there to stop it spinning while you start the bolt, not to carry load.
- Drilling the cross dowel hole slightly off line — The bolt then catches the edge of the barrel, cross-threads or simply will not enter. Mark both holes from the same face and drill the barrel hole square.