Hi Pat,
A possible source for the hardware you are seeking may be a well stocked electronics supplier, like Radio Shack in North America. In the past, they had a good selection of fine thread nuts and bolts in various sizes, but I don't know their current inventory status. Another source may be an upper end model railroad parts supplier, in the past I remember a brand (Grant???) with a line of very small precision brass hardware - some being very small.
To better illustrate what I did, here are some photos:
The first shows the bolt just by itself passing through the hole in the deck and threaded a few turns into the nut under the deck. The nut was secured with a few pieces of styrene and superglue before the deck was cemented to the hull. This is a simple rig intended for a minimum of threading and unthreading only - it is not a robust design, just enough to secure the conning tower properly in place without using any adhesive.
![](http://s28.postimg.cc/tepw627gt/conningtowerbolt1.jpg)
This next image shows the bolt fully threaded in place with the conning tower (still in primer). A thin nylon washer helps to more evenly spread the pressure of the bolt to the conning tower.
![](http://s14.postimg.cc/42kfnnm01/conningtowerbolt2.jpg)
The last image is of the set up from above. The head of the bolt sits flush with the deck and will be covered by the periscope housing.
![](http://s4.postimg.cc/z81zsvwl9/conningtowerbolt3.jpg)
I still need to fill in the old Amati conning tower outline in the brass deck as it does not exactly conform to the modified Revell conning tower footprint. I think I will try some very thin styrene strip and superglue, then carefully sand it level with the rest of the deck.
Cheers,
Bill