Duramaxx BigBig Box Manual page 12

Step 5
Fit the ball coupling (13) to the handle section (4) of the
tow bar. Use the two 3.5 cm-long M6 screws (16) for this
purpose.
Step 6
Secure the saddle-support mounting (12), with the help of
the plastic shims (17), to the saddle pillar of your bicycle.
Now use the screw (18) that is ready-fitted to the saddle
support mounting (12) to attach the ball-head coupling (11)
to the saddle support mounting (12).
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