I have no idea what these are used for. I assume that they are somthing to do with engineering but I may well be wrong.
The wooden box is quite old & was obviously made to contain the shims.
The thickness is around 0.012" but I only have a rather questionable vernier to measure them with so I may be a bit out.

I have no idea how many there are. What you see in the photographs is what you get.