The drive train of the Tiger 1 included a final reduction gearing that brought the high revs of the engine down to the ponderous wheeling of the sprocket, while of course scaling up the torque. This gearing was located in a sealed, cast housing placed outside the hull, partially enclosed by the sprocket wheel itself. You can buy a photo of these housings .
A shallow recess was made in each front hull side to take this housing. A curved steel piece, 80mm thick, was bent around its front edge to protect it. You can buy a photo of the recess .
The above diagram shows the recess on the left hull side. The small circle at top right is a hole in the armour, through which the drive shaft emerged. The gear housing was fixed in this recess by 16 (left) or 17 (right) bolts, some of which were permanently sealed in place because the hull front plates did not allow their removal. On the reverse side of this hull wall, some bolts terminated inside the hull and others outside. At bottom right of the diagram you can see that one of the bolts for the end plate of the foremost torsion bar lies within the recess, and a notch is made for it. A special short bolt was used in the torsion bar at this point to avoid fouling the reduction gear housing. Also, one bolt was omitted from the housing itself; as you can see, the hull has no hole for it.
The above diagram shows the outline of a reduction gear housing, as seen from outside the tank. It's interesting that the same housing could be used for either the left or right, requiring only that you switch a small oil inlet pipe from one side to the other on its inner face. At one point on its edge there's a small indentation, which is necessary to clear the foremost swing arm on the right side. A bolt hole is moved slightly to make room. This indentation is present on both housings, even though it has no purpose on the left side.
[1] Survey of vehicle 250122, Bovington, by David Byrden
[2] Survey of vehicle 250122, Bovington, by John Desaleux
[3] Survey of vehicle 251114, at Saumur, by Jean-Charles Breucque
[4] Der Panzerkampfwagen VI und seine abarten, Walter J. Spielberger, Motor Buch Verlag