bolt

Bolt is a term with several distinct meanings, including a mechanical fastener, a stream of atmospheric electricity, and a rolled length of fabric. Each sense belongs to a different domain, and the word is used in technical, industrial, and everyday language.

A bolt as a fastener is a cylindrical metal shaft with external threads and a head. It is designed to be tightened with a nut or into a tapped hole, converting rotational torque into clamping force. Bolts come in numerous shapes, such as hex, carriage, shoulder, and eye bolts, and in materials including carbon steel, stainless steel, and alloy steels. Finishes such as zinc plating, galvanizing, or black oxide protect against corrosion. Standards for bolts include ISO metric (M6–M30) and the Unified Thread Standards (UNC/UNF). They are widely used in machinery, automotive, construction, and furniture.

A bolt of lightning is a sudden electrostatic discharge that occurs between clouds or between a cloud and the ground. It produces a bright flash and thunder and involves a conductive channel that can carry millions of amperes at voltages reaching hundreds of millions. The process often begins with a stepped leader and culminates in a rapid return stroke. Weather conditions influence frequency, and safety practices advise seeking shelter and avoiding tall objects during storms.

A bolt can also refer to a roll of fabric or textile material wound on a bolt, typically sold by yardage. Cloth widths commonly range from about 44 to 60 inches, though variations exist for specialty fabrics. Retailers quote yardage per bolt, and the length depends on fabric type and market specifications.

Other uses include the verb form meaning to dash away or to swallow quickly. The term also appears in brand names and technical terms, such as bolt-action mechanisms in firearms or product names in technology contexts.