This 37mm adapter allow you to install SESTO SENSO 2 on focusers that come with 37mm diameter large shaft, like the 3,5" FeatherTouch and FSQ-130 (or other focusers with 37mm diameter large shaft). SESTO SENSO 2 as standard connects to focusers that comes with 25mm diameter shaft (that are the most of the focusers on the market): in order to connect it to focusers that comes with 37mm diameter large shaft, you need to add this adapter.
This 37mm adapter is installed on the focuser instead of the 2 knobs (macrometric and micrometric), then you can install SESTO SENSO. Together with this adapter, you will find in the package the longer bushing that is used to connect SESTO SENSO to the focuser. You will also find installation instructions (in english and italian).