kruvide

Kruvide (Estonian for screws) are a broad category of fasteners used to join components by threading into materials. They typically have a shaft with helical threads and a head that provides a driving surface. Turning with a screwdriver or power bit engages the threads, drawing the parts together and creating clamping force.

Common types include wood screws, which have a tapered shank and relatively coarse threads; machine screws, designed to mate with a nut or tapped hole; self-tapping screws, which form their own thread in softer materials; self-drilling screws, which drill their own pilot hole; lag screws, long heavy-duty fasteners for wood; sheet-metal screws for metal substrates. Head shapes include flat (countersunk) to sit flush, pan and round for more clearance, and hex for high-torque applications. Drive types range from slotted and Phillips to Pozidriv, Torx, and other star designs.

Materials and coatings: carbon steel is common, with zinc plating or galvanization for corrosion resistance; stainless steel offers higher resistance in harsh environments; brass and aluminum are used for specific properties. Finishes include black oxide and polymer coatings.

Sizes follow metric (diameter in millimeters with ISO thread pitch) and imperial (diameter in inches with thread count). Standards organizations include ISO, DIN, ANSI/ASME, and ASTM.

Installation considerations: select appropriate type, size, material, and thread; use correct pilot holes when required; choose head and drive for the application; avoid over-tightening and consider corrosion protection, withdrawal and shear loads.