About this detail of the Tiger
In the original cupola design for the Tiger, the top flat ring was held in place by 10 bolts, equally spaced around its edge.
This German-drawn cross section shows one of the bolts. It goes into a threaded hole in the main armour ring of the cupola. There is no possibility of using a nut here; the hole is not accessible from underneath.
This is one bolt in a real cupola. As usual, there is a locking disc under the bolt head, bent into shape to hold it in place.
This is how the same item is represented in popular model kits; Dragon above, and Rye Field below. It's clear that both manufacturers have represented a nut instead of a bolt; there is a short length of bolt tail protruding through.
You can increase the accuracy of your model by sanding down these items to represent flat bolt heads.