Assembly screws are also called "book screws" or "sex bolts", and are available in both metal and plastic versions. Years ago our suppliers used to include a metal set with their wings and when these proved problematic they later switched to a plastic set, but have not included either for a long time because assembly screws are often counterproductive.

The plastic assembly screws can be used to attach the wing directly to a hard metal backplate when rigged for a single tank without a single tank adapter. Note that this function is just cosmetic, omitting the assembly screws does not cause a problem. Without the assembly screws, when the BCD is taken off a single tank, the wing will hang loose on the cam straps.

The metal assembly screws can be used to attach accessories to the holes on edges of metal backplates, but in our opinion the plastic ones actually work better. Don't be concerned about the strength of plastic vs metal; the plastic version is plenty strong for these applications plus they are not subject to galvanic action and don't cause wear on materials rubbing against them.