Inertia Block

This is the name for a heavy weighted metal block placed under a guitar’s bridge to enhance either sustain or tone — or both. The first guitar ever to use this effectively was the Fender Stratocater, developed in 1954. However, the largest block was probably the massive chunk of solid brass that Yamaha placed under the bridge and tailpiece of its SG2000, the double cutaway guitar that Carlos Santana used for many years (and which gave Yamaha a nice shot of credibility within the guitar community).