About this detail of the Tiger
Each crew member in a Tiger was provided with a gas mask, in a canister that could be used to carry the mask when outside the tank. In practice, gas was not used as a combat weapon and these masks were not needed.
German tanks normally had these canisters stowed inside, accessible for immediate use. Since the Tiger's turret was designed for three men, three canisters had to be stowed in it. There was a standard holder for the canister; it was attached by two screws to the tank.