Sena M1 EVO Quick Start Manual page 7

QUICK START GUIDE
5. Secure the excess strap with O-ring and then attach
the chinstrap pad.
6. Turn the retention system knob clockwise to tighten
or counterclockwise to loosen.
7. To change the height of the retention system, firmly
pull or push the retention system upward or
downward to a different position.
Retention System Knob
WARNING: For maximum protection, this helmet must be fitted
and attached properly to the wearer's head in accordance with the
following instructions. If after adjustment the helmet does not fit
properly, do not use the helmet. Return it to the retailer or Sena.
Note: Check the chinstrap's
position and tension regularly to
ensure proper fit.
Retention System