US Patent 7134149 Face mask for diving

Here is disclosed a face mask provided with a rotation angle regulating means for stepwise variation of an angle of each buckle relative to associated lens frame side wall. A buckle is rotatably attached to the lens frame side wall of the face mask and the lens frame side wall and the buckle are formed with the rotation angle regulating means comprising one or more protrusions and depressions adapted to be releasably brought into mutual engagement.