This is a complete replacement bridge set for Fender USA guitars from Callaham. It's a standard Stratocaster model with a string spacing of 11.3mm. Normally it comes with a steel block, but this is a special order model equipped with a brass block. Of course, it's a genuine Callaham block. Compared to the steel block, it has a bit more weight, so it sustains longer than the steel version. Also, the sound's center of gravity is slightly lower, giving it a more mellow sound. Callaham bridges have a slightly hard and high-pitched sound by default, so I personally recommend this brass block specification.