The stock steam valve knob on the Gaggia Classic Pro espresso machine is very glossy and slick. This makes it difficult to grip and control. This model is a simple ring with a knurled pattern that fits over the steam valve knob and is pressure-fit. It greatly improves the grip of the steam valve knob. It may also fit the original Gaggia Classic (non-pro model), however it has not been tested on that model.
The author hasn't provided the model origin yet.