Hello,
Your are getting deeper and deeper!
When one is making plastic scale model such issues are not always very important.
OK, let?s try to get some answer to you.
The ?nose? section- an airframe from spinner root to the backseat of cockpit was covered with 12 detachable plates (including cowlings and backsides of cockpit) with the locks type ?Dzus?. Sorry I have no the right name for it in English, but I have attached the cross-sectional and plane views of it.
Already being in serial production due to complains from front the cowling fixing was changed to a new squeeze lock , the one like used on Bf109. This was introduced from the 16th series of production.
The rest wooden airframe was covered with glued birch plywood of 5 layers (0,5mm each).
The central plane of the wing was covered with aluminum sheets and attached to frame by means of the screw bolts that helped for quick service and maintenance during the combat periods.
The rest of wings where covered like the wooden airframe- glued with the 5layers of birch plywood.
The connection of wings with central-plane was covered with metal plate that was fixed with anchor-screws.
Checking the pictures I would say that the screws and bolts were countersunk type.
BR Audrius