Sena R1 Quick Start Manual page 6

QUICK START GUIDE
4. Adjust the chinstrap tension at the buckle
so the chinstrap is tight and comfortable
by pulling the chinstrap end through
the buckle to either tighten or loosen as
needed. Use the "O-Ring" to secure the
excess strap.
Chinstrap
O-Ring
Note: Check the chinstrap's position and tension
regularly to ensure proper fit.
5. Turn the retention system knob clockwise
to tighten or counterclockwise to loosen.
Retention System Knob