About this detail of the Tiger
The Tiger's turret was supported by a flat steel ring, welded to the inside base of the turret. This ring was made of two parts. The diagram above shows the size of the assembled ring.
The weld lines between the parts are drawn at left and right. In the second type of turret there were bolt holes at the midline, so the welds were offset slightly as you can see here.
This profile shows how the ring was welded to the inside base of the turret wall. The ring tapers from 30mm at the outside to 14mm at the inside edge, to fit the equipment attached underneath it.
The ball-bearing race was attached to the underside of this ring by bolts spaced evenly around it. They passed through smooth holes in the ring. (There were other holes in the ring, for example to attach the gun counterbalance; they are not drawn here.)
This photo of the Bovington vehicle  shows two of the bolt heads.
At the front of the turret the ring was welded to the chin armour, which was 5mm lower. The four holes in the front of the ring did not carry bolts with protruding heads; instead they had large screws, sitting flush inside the ring. This was to avoid fouling the gun mantlet. This profile shows the ring, the chin armour and a screw hole.
The turret ring bolts tended to break when the turret was hit by enemy fire. Therefore additional bolts were put in the ring, in the spaces between the existing bolts, starting at Turret #201 in April 1943 [1, see 126.96.36.199] .
This diagram shows the ring in the second type of turret. Some of the possible bolt positions are unused, because they are blocked by equipment attached to the turret ring.
The Turret Manual describes this arrangement; "The rotating outer ball race (Outer Ring) is seated in the turret support ring and fixed to it by 34 hex screws and 7 cylindrical screws." [3, see 2.(b)2 ]
The Tiger's underwater travel capability was omitted from August 1943. With the deletion of the rubber seals the support ring was given a simpler profile, now being 20mm thick at the inner edge.
This workshop drawing shows a profile of the front center of the turret base. The support ring and a screw hole are shown. Also shown is an M6 threaded hole for attaching the cowling.
Another improvement was the use of 'impact sleeves' that held the bolt heads 10mm clear of the surface. These metal sleeves could absorb an impact by distorting, and after the battle the crew could simply tighten up the bolts. I don't know when these sleeves were introduced.
All bolts on the Tiger had metal tabs to prevent them working loose. In this case, because of the impact sleeves, the tabs sat 10mm above the surface. They were flat rectangular strips of metal, 40mm by 175mm, looped over each pair of bolts with their corners bent upwards. The photo shows a museum vehicle built in April 1944 (the green paint is not original).
This diagram shows all of the bolt holder tabs that were needed. It also shows the various items that blocked 7 of the bolt positions: the commander's seat and the 'bridge' were bolted to the ring, and base plates with threaded holes for other items were welded on at various points.(The latest version of this article)