Overview
A cross dowel, also called a barrel nut, is a short cylinder with a threaded hole across its middle and a slot or cross in one end so it can be turned. It sits in a cross-hole in one board, aligned with a bolt hole drilled into the board's edge or end. A bolt passes through the second board, enters the first, and screws into the nut. Tighten the bolt and the two boards pull together. The nut and its hole stay hidden inside the wood, which is why the type is so common.
Types and sizes
- Standard cross dowel: a steel or zinc cylinder, often 10 mm (3/8 in) in diameter by 15 mm (5/8 in) long, M6 thread.
- Heavier barrel: 12 to 14 mm (1/2 to 9/16 in) for M8 and larger bolts.
- Bolt: M6 or M8, in lengths to reach the nut: normally 40 to 100 mm (1-1/2 to 4 in).
- Slotted-end nuts turn with a screwdriver to line the thread up; dowel-style types use a hex socket.
- Cover cap: a plastic or wooden disc hides the bolt head.
Where it is used
Knock-down carcase furniture, cot and bed frames, desks, benches and table rails to legs. Danish and mid-century American designs for flat-pack shipping used bolts of this kind. They are also used for attaching a table apron to a leg without visible fixings.
Choosing and sizing
The bolt's axis must pass through the centre of the cross-hole. Place the nut about 30 to 40 mm (1-1/4 to 1-1/2 in) from the end of the board, and measure the bolt to the nut centre. The cross-hole diameter should be about 1/3 of the board's thickness: a 10 mm (3/8 in) nut fits 19 mm (3/4 in) stock, but a 12 mm nut is safer in 25 mm (1 in). Use two bolts per joint at least 50 mm (2 in) apart.
Installation
- Mark the bolt axis on the board edge or end, 30 to 40 mm (1-1/4 to 1-1/2 in) from the end.
- Drill the cross-hole for the nut across the board's face, with a brad-point or forstner bit matching its diameter, to a depth that centres it on the axis line.
- Drill the bolt hole in the other board, then through the first board's edge, using the first as a guide.
- Drop the nut into the cross-hole and turn it with a screwdriver so its thread faces the bolt hole.
- Pass the bolt through and tighten with a hex key; re-check the joint after a season.
Wood movement and species
The nut sits across the grain of the first board. Shrinkage in width can slide the nut off the axis and make the bolt cross-thread; keep the nut near the board's edge where it moves least. Quarter-sawn stock is more stable. In Hard maple and Black walnut the joint stays tight; in Eastern white pine and Yellow poplar the nut can crush the fibres, so use a bigger washer. In MDF (medium-density fibreboard) and Particleboard edge screws are weak, which is why a bolt is the better choice.
Common mistakes
- Cross-hole not on the bolt axis: the bolt hits the nut's side.
- Bolt too long or too short for the nut.
- Nut thread facing the wrong way.
- Over-tightening, which crushes the wood around the nut.
Related
- Bed rail fastener: the usual bed-specific alternative.
- Threaded insert: a nut set in the end of the board.
- Machine screw and T-nut: a screw and nut that go through the board's face.
- Confirmat screw: a one-piece fixing for sheet goods.
Styles it suits
Suitable for
Fixes into: hardwood, softwood, sheet, engineered.
Sources
Updated 2026-10-03. Sizes and ratings are typical trade figures drawn from the sources above. A load rating is the maker's rating for one product, not a property of the type: check the maker's own sheet, and test a fit on scrap before cutting good wood.