Cartoon rocker stick figure holding a guitar in one hand and a bell-shaped truss rod cover in the other hand — representing a blog post about the Gibson Bell Truss Rod Cover shape mark trademark registration.

Trademark: Gibson Bell Truss Rod Cover

First Used: 1922

First Registered: 1975

Current Owner: GIBSON, INC. [1]

Trademark Type: non-traditional trademark; trade dress; shape mark

Primarily Associated With: string instruments [2]

Brief (and likely incomplete) History [3]:

One of the more important innovations to the modern guitar occurred in the early 1920s, with the creation (and patenting) of the adjustable truss rod. As steel guitar strings became increasingly common, their greater tension created a problem for instrument makers: over time, the pull of the strings could cause a guitar’s wooden neck to bow or warp, affecting both playability and intonation. Gibson employee Thaddeus “Ted” McHugh developed the adjustable truss rod to help address that problem. His design placed a metal rod inside the guitar neck that could be tightened or loosened to counteract string tension and adjust the curvature, or relief, of the neck. Unlike earlier fixed reinforcement methods, the adjustable rod gave players and repair technicians a way to compensate for changes in the neck over the life of the instrument.

Gibson began installing the adjustable truss rod in instruments around 1921–1922, with the adjustment nut accessible at the headstock. That access point needed to be covered, which created the need for a removable truss rod cover. Gibson’s solution was a small black cover plate featuring a distinctive outline that widened near the top before tapering toward the bottom (creating what later became known as the Gibson Bell Truss Rod Cover shape mark). Unfortunately, why Gibson originally selected the bell shape does not appear to be documented. What began as a functional part, however, became a recurring visual feature on Gibson instruments. Although the exact appearance of the cover varied over the years, including versions with contrasting borders, engraving, and model names, the basic Gibson Bell Truss Rod Cover shape mark has remained constant over the last 100 years.