This 26mm adapter allows you to install SESTO SENSO 2 on focusers that come with a 26mm diameter shaft, like focusers from Explorer Scientific (or other focusers with a 26mm diameter shaft). Out of the box, SESTO SENSO 2 connects to focusers that come with a 25mm diameter shaft (the most common diameter on the market). In order to connect it to focusers with a 26mm diameter shaft, you will need to include this adapter.
This 26mm adapter is installed on the focuser instead of the 2 knobs (macrometric and micrometric), then you can install SESTO SENSO 2. Together with this adapter, you will find in the package the longer bushing that is used to connect SESTO SENSO 2 to the focuser.