The BH77A replacement bayonet lens hood is specifically designed for use with the Tokina ATX AF 11-16mm F/2.8 PRO DX lens.
The "A" version of the hood has a black felt lining on the interior side of the hood where as the "B" version does not. The felt dramatically reduces the potential for light bouncing off the interior wall of the hood for increased contrast but tends to pick up dust and other small particles from the air and the camera bag.