Overview
A back-flap hinge has two wide leaves, one longer than the other, with a knuckle off-centre so the leaves fold flat together. It is screwed to the underside of the table top and leaf so the leaf can drop. The knuckle is positioned so the leaf swings on the same axis as the rule joint, the pair of matching cove and quarter-round profiles on the edges of the top and the leaf. When the leaf is raised, the joint closes tight; when it hangs, the rounded edge swings clear.
Types and sizes
- Back-flap hinges are made with square or shaped leaves; rule-joint hinges are the traditional pattern.
- Size is leaf width and length: 1-1/2 x 3 in (38 x 75 mm) for small drop-leaf tables, 2 x 4 in (50 x 100 mm) for dining tables.
- Brass is usual on period furniture; steel on cheaper tables.
- A flush pair of countersunk screw holes to be recessed into the underside.
Where it is used
Drop-leaf, gateleg and Pembroke tables in William and Mary, Queen Anne, Hepplewhite, Federal and Sheraton furniture. The rule joint was a defining detail; the hinge type is the working part of it.
Choosing and sizing
Use two hinges on a leaf under 600 mm (24 in) long and three or four on longer ones, spaced about 75 mm (3 in) from each end. The leaf's thickness sets the rule-joint profile and the hinge's knuckle position; match the hinge to the joint, not the other way round.
Installation
- Cut the rule joint profiles on the top and leaf edges first: a quarter-round on the top, a cove on the leaf, sharing a pivot centre.
- Lay the top and leaf face down with the profiles closed tight.
- Place the hinge so the knuckle centre aligns with the pivot centre of the rule joint, and trace the leaves and knuckle.
- Chop the recess so the leaves lie flush with the underside and the knuckle sits proud in a clearance cut.
- Fix with screws; check that the leaf swings freely and closes without a gap.
Wood movement and species
A solid-wood top moves seasonally across its width; the leaf must have clearance for the hinge to work, so leave an extra 1 mm (about 1/32 in) gap at the leaf's free end for changing humidity. Choose a rule-joint profile that tolerates a slightly open joint. Brass hinges avoid stains in Black walnut and the oaks. Seasonal change in a wide leaf can split screws in end grain, so screw into face grain.
Common mistakes
- Knuckle not aligned to the rule-joint pivot: the joint binds or leaves a gap. Dry-fit before final fixing.
- Recess too shallow so the leaf lifts away from the underside.
- Single large screw per leaf: use all the holes.
Related
- Butt hinge: general-purpose alternative.
- Piano hinge: continuous alternative for modern tables.
- Wood screw: fixing the hinge.
Styles it suits
Suitable for
Fixes into: hardwood.
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.