I think that's about 8 mils (0.008) in inches which is maybe a little thick -- but hey, if it's free, try it!

My last couple of pinhole plates were made with 1 mil brass shim stock which is admittedly pretty hairy to work with. In the past I've used 2 mil, which is easier to handle and still works well. A few hobby shops and even some art supply stores carry assortments of brass widgets for model making, K&S is a brand, that includes a pack of 3 or 4 thicknesses of brass shim stock.

The ideal pinhole is a knife edge -- a hole in an infinitesimally thin sheet!