| 摘要 |
Improved chin rings are disclosed, wherein a chin ring may comprise a substantially circular chin ring having an outer surface and a slot, a first radially spaced aperture in the chin ring on a first side of the slot, a second radially spaced aperture in the chin ring on a second side of the slot, a first louver disposed at least partially over the first radially spaced aperture, the first louver disposed at a first angle relative to the outer surface and a second louver disposed at least partially over the second radially spaced aperture. |
