I have taken two thinner feeler gauges to give me the thickness that I have needed when I did not have the correct feeler gauge.

Example: I would combine together a .024 and a .026 feeler gauge to use as a substitute .050 feeler gauge.

Example: I have even used a .024 with a .025 for a .049 when I needed a .050 because that was the closest I could make do with what I had to get .050.