Sena X1S Quick Start Manual page 8

QUICK START GUIDE
4. After removing the chinstrap pad, adjust
the chinstrap tension at the buckle with
the strap adjuster in the proper position.
Adjust the tension so the chinstrap is tight
and comfortable by pulling the chinstrap
end through the buckle to either tighten
or loosen as needed.
5. Secure the excess strap with O-ring and
then attach the chinstrap pad.
Note: Check the chinstrap's position and tension
regularly to ensure proper fit.
Chinstrap Pad Chinstrap
O-Ring