It is a drop-in replacement for a stock tremolo in a Fender Stratocaster. It was designed to improve tuning stability compared to the stock Fender tremolo.
The "SB" in the model name refers to the steel block which helps to magnify the overall sustain, brightness and top end, resulting in a more expansive tone.
The "5+1 hole" designation refers to the fact that the top mounting hole is round to locate the vibrato laterally, while the other five holes are elongated to reduce the chance of the screws binding, which allows the tremolo to "return to zero" more accurately resulting in improved tuning stability.
This model is similar to the more expensive Wilkinson/Gotoh VSVG tremolo.