Ironmongery (or hardware) describes metal components used to connect materials, including moving parts such as door hinges. In the early 2000s most hardware was imported.
Machine-produced nails were cut from flat plates of metal by machine. Known as type-B nails, these were imported until the end of the 1800s, when wire nails almost completely replaced them. Wire nails are made by feeding steel wire into a machine which, in one operation, holds the wire and cuts it, and forms the head and chisel point – all at the rate of several thousand nails a minute.
Nails work by shear strength, so that the nail resists being pulled from its bed. The shear strength of the nail can also support a very great weight.
Steel nails used for exterior work are galvanised by coating them with a thin covering of zinc, which oxidises, protecting the steel.
Compressed-air-powered nail guns are widely used in the building industry and have sped up construction. They are used to secure framing timbers together, and for nailing timber to other materials such as concrete or steel, using special high-tensile steel nails. Staples are also widely used instead of nails to secure sheet materials.
Screws are metal pins with a groove shaped like a corkscrew cut into the surface of the shaft. There is an enormous range of screw types, but their purpose is to join materials together. Different kinds of screw are used in timber, metals and plastics.
Wood screws are tapered so that they can penetrate wood without the need to drill a hole – although it is usual to drill first. The tapered shaft means that the screw fits increasingly tightly as it is turned.
Heads of traditional wood screws were originally slotted, with a recessed groove in the surface, but in 1908, a square-drive screw head was invented, followed in the 1930s by the Phillips head screw. Also invented around 1900 was the hexagonal head or Allen Key screw. These screw types have all been imported for use in New Zealand building.
Nuts and bolts
There is a range of shapes used for bolt heads and nuts, but the most common is hexagonal. Square-headed bolts are also common. Round-head coach bolts have a hemispherical head, with a square shank beneath which prevents the bolt from turning as the nut is tightened.
Bolts are similar to machine screws, but are much thicker and longer. Bolts have a shaft with parallel sides and a uniform thread along all or part of the shaft. A bolt needs a hole which is just large enough to allow the shaft to be pushed through, and it relies on a nut to secure the connection by being wound tightly against the material being joined. A circular disk known as a washer spreads the force of the bolt so that the material is not crushed. Through friction it also resists the likelihood that the nut will come undone.
A vast array of specialised components available for building includes brackets, cleats, straps and other metalwork. Special brackets are used to strengthen joints between pieces of timber. Metal strap is nailed over framed walls and roofs to brace them and prevent them moving under load. Heavier metal brackets can be cast into concrete to support timber posts.
Nail plates are flat strips of galvanised steel which have been punched to create multiple small prongs on one side. These are hammered into the surface of adjacent pieces of timber to hold them together. They are widely used in framed structures and in the prefabrication of structural elements such as trusses.