Siemens SIDOOR ATD401W System Manual page 194

Geared motors
5.2 Installation
3. Pass the toothed belt over the deflector pulley and drive pinion. Place both open ends of
the toothed belt in the door clutch holder. Screw the door clutch holder together.
ATD4xxW Door Controller for Industrial Applications
194
System Manual, 01/2017, A5E38080677-AB