Is it the thickness in the compressed or uncompressed state?
I have an 3/4" SPH pad that, brand new, measures 1", but if I squeeze it between my fingers, it measures 3/4". So SPH seems to use the compressed thickness.
I also tried a Toklat T3 Matrix that comes with 1/4" felt shims. They might be 1/4" uncompressed, but half that when compressed. So Toklat uses the uncompressed measure for their stuff. It is definitely not 1/4" compared to thinline shims (which I have from my english saddle) – those are definitely 1/4" and don’t compress easily.
I know the answer is likely “no,” but is there a standard?