This is the Primary spindle on MASSO and is not included as part of the Multi-Head settings menu.
This spindle is the main reference coordinate for the offset of the 4 Multi Spindles.
The main spindle uses tools 1 to 100 and can be used with your tool changer.
This spindle is configured under the F1 screen using the Main Spindle tab
There is a Main spindle TTL output that can be configured when used with the Multi Spindles 1 to 4 but if this is the only Spindle installed it is not needed.