It is a cap for the Nitecore LA10. It is used to keep the light from going into the eyes directly when the torch is turning out and used in the darkness. This will give the eyes a comfortable lightness when look from behind of the torch.

The test turns to be very positive, especially when the body of the cap is printed with black primer. There is almost no light leaking at the back, as shown in the picture, which gives a very comfortable using experience.