There was a direct vision port on both sides of the Tiger 1's turret. A round hole of 170mm diameter was cut for it; the designers apparently preferred round holes because, having no corners, they collected the least possible stress in the armour. The same design of vision port was present on the hull of the Ferdinand vehicle for which the turret was originally designed.
A mushroom-shaped plug filled this hole, 210mm wide on the outside.
For vision, a tapered slot was cut through the plug.
This slot was tilted downwards by 2.5 degrees, so it emerged on the outside slightly below the center line.
When installed in the turret wall, the plug was welded solidly on the outside.
The inside was fixed by two steel shims inserted into slots above and below. These shims were very tight-fitting; in the vehicle at Bovington they had to be shaved down slightly to fit (the steel plate for the turret wall was probably thicker than designed). The shims were welded into place, so the plug could not be removed.
[2] Survey of vehicle 250122, Bovington, by David Byrden
[3] DW to Tiger 1