Take it to a machineshop and see if they will check the thicknesses w/ a micrometer.
mike

1 may be equal .001, if so this would be thinner than sheet of paper. so if 1 is like sheet of paper except thinner then it's .001. .1 would be .100 thousands which would be 100 times thicker than piece of paper. Should be obvious. .002 should be marked on the feeler gauge and so on which is about as thick as sheet of paper. Very few feeler gauges start out at .001 that's very thin, usually that start out at.0015 which is 1 and 1/2 thousands. half of a sheet of paper.

Most common sets of feeler gauges go from .001 to .025. To get 1 you would have stack enough to get one full inch thickness. if you see dicmel point in front of the 1 it would be .1 or .100 or .1000 you would have to put about 5 togather to get that thickness from standard set of feeler gauges.

Might also be MM

I agree probably metric. 1mm approximately .004.

I MM is .03937".
.004" is about 0.1 MM!!!!

Thanks for all the responses. My brother got tired of laying around and dug out my feeler gauge and returned it. At the same time I had errands in town And dropped by a machine shop to see what I had. No Idea. "1" is neither .oo1" or 1mm something in between. Chatting with the guy, I remembered that the fellow who gave me this was a retired machinist who worked for a company who specialized in aluminum parts for airplane engines. He theorized that it was a special gauge for setting up some mill or something. Dunno.

Thanks again,

Ev