frame rail

Noun

frame rail (plural frame rails)

1. Each of the two main longitudinal structural members of a body‑on‑frame vehicle, running parallel front to rear and supporting the chassis, to which cross‑members, suspension, drivetrain, and body are attached.
   • It has been proposed that the length of the middle, parallel portion of the sub-frame comes flush with the inner side of the lower flange of the main frame rail.1912 November 27, P. M. Holdt, “The Gasoline Automobile — Its Design and Construction.”, in The Horseless Age., volume 30, number 22, page 833
   • Instead of a relatively flat, ladder-like structure with two longitudinal, parallel frame rails, it consists of a central, strong tubular backbone (usually rectangular in cross-section) that carries the power-train and connects the front and rear suspension attachment structures.2025 March 24, Wikipedia contributors, “vehicle frame”, in English Wikipedia, Wikimedia Foundation
2. A horizontal structural member of a furniture frame, typically joining the legs or vertical posts, providing support and rigidity; commonly found in tables, chairs, cabinets, and beds.
   • The frame rails must be firmly mortised into the legs to ensure stability.1901, Frederick Thomas Hodgson, The Practical Cabinet Maker and Furniture Designer, page 212