A rigging screw (or bottle screw/turnbuckle) is a mechanical tensioning device used in a sailboat's standing rigging to tighten and adjust shrouds and stays. It consists of a central, threaded body with two opposite-threaded eyebolts, jaws, or studs that draw in or out to adjust tension as the body turns.

Key Details of Rigging Screws
Purpose: They provide necessary tension for the standing rigging (wire rope supporting the mast) to keep it secure and maintain correct mast shape.

Mechanism: One end is threaded left-handed and the other right-handed; turning the central body adjusts both simultaneously for increased or decreased tension.

Components: Frequently used with toggle terminals to prevent bending loads on the rigging screw.

Materials & Types: Typically stainless steel (common/economical) or bronze (self-lubricating, better for preventing seizing).

Alternative Names: Known as a bottlescrew or a turnbuckle.