Looks like little (I think metal) wafers, used to measure/compare thicknesses. (Presumably) One for 1/32", one for 1/16", etc etc. Principally used by machinists?
I saw them described in a Woodsmith years ago, thought "I've needed those for years!" and *thought* I'd remember the name and get around to finding a source eventually. Hah! :-)
Ring any bells?
Thx, Will