strap
A narrow strip of anything, as of iron or brass.
strap: the reinforcing strip that holds wood joints together
In carpentry, a strap is a narrow band of metal, typically steel or iron, fastened across a joint or seam to reinforce it and distribute stress. The most common strap is the metal strap or mending plate, which bridges two pieces of timber and is bolted or screwed through both members. A typical strap might be 40 to 100 millimeters wide and 2 to 5 millimeters thick, with multiple holes drilled to accommodate bolts or screws spaced at regular intervals.
Straps appear wherever carpenters need to arrest movement or add strength to joints that might otherwise separate or flex excessively. A roof truss will have straps bolted across its web members to prevent buckling under load. A timber frame connection where a beam meets a post may use straps on both faces to resist tension or shear. Straps also work on plumb, keeping cracks in large timbers from spreading; a crack in a beam running perpendicular to the grain is sometimes restrained by screwing a strap across its width.
Variants and installation
Different joint conditions demand different strap profiles. A flat strap lies flush on the timber face; a corner brace is an L-shaped strap that reinforces right angles; a T-strap handles T-shaped junctions. Stainless steel straps resist corrosion in damp conditions and exterior work, though they cost more than galvanized or painted steel. The number and spacing of bolts or screws depend on the load and the strap length; closer spacing increases the effective clamping across a wide joint or crack.
The strap's success depends on the fasteners being tight and the strap making full contact with the timber along its entire length. Timber that has shrunk or warped after the strap was installed will leave gaps that undermine the joint. For this reason, straps are often installed after the structure has aged and movement has stabilized, or they are part of the original design when static joints are unavoidable.
The term strap extends beyond metal to include cloth or synthetic tape straps used in some applications, though metal straps remain the standard in structural carpentry. When a carpenter specifies a strap repair, they mean a deliberate structural reinforcement, distinct from a bracket, which adds support at a corner, or a tie, which is hidden within a wall cavity. A strap is visible, temporary or permanent, and communicates clearly that the joint it crosses needed reinforcement.