Boltthrough

Boltthrough, sometimes written bolt-through or through-bolting, is a fastening technique in which a bolt passes completely through one or more parts and is secured with a nut on the opposite side. The term is used across woodworking, metal fabrication, and automotive applications. In a typical boltthrough joint, holes are drilled through all members to be joined, the bolt is inserted, and a washer and nut are tightened to clamp the parts together. This arrangement distributes shear and withdrawal forces over a larger area and allows precise alignment of components.

Materials and hardware commonly used include steel or stainless-steel bolts, hex or carriage bolts, washers, and nuts, with locknuts or nylon-insert locknuts for resistance to loosening. Through-bolts may be used with or without countersinking, depending on design requirements and aesthetics. In wood, through-bolts often exit the far face and are secured with a large washer and nut; in metal assemblies, the bolt may pass through flanges or mounting brackets.

Applications include timber-frame construction and furniture joinery, where through-bolting yields strong, disassemblable joints; automotive and machinery mounting brackets; and equipment that requires easy field maintenance. Advantages include high clamping force, simple installation, and reliable load transfer through multiple members. Disadvantages include the need for access to both sides for tightening, potential protrusion of hardware, and higher risk of joint loosening if not properly secured in environments with vibration.

See also: through-bolting, bolted joint, carriage bolt, locknut, washer.