An adjustment mechanism for allowing a user to adjust a length of a headband includes a stationary case, a clutch, and a knob. The stationary case defines an opening and a circular recess. The clutch includes a cam arranged within the circular recess and a pinion extending axially from the cam such that the pinion is positioned outside the case via the opening to engage with the headband. The clutch also includes a roller located adjacent to a first cam portion of the cam. The knob has an actuating element arranged between the roller and a tab of the cam. The knob is rotatable in a first direction for allowing the user to shorten the length of the headband. The knob is rotatable in a second direction allowing the user to increase the length of the headband.
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