feeler gauge. I wish I could remember where I saw the tolerance for this. You are correct that it's less than 1/16th. Its probably half that or less, but you don't want to have the axle retaining clip under pressure, so play is preferable to having it too tight. I am putting flex discs in my 84 this morning and it has original axles. There is play on one of them, but its not much and not enough to make noise.

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1985 300 TD 448K
1984 300 TD 278K

1983 240D euro 240k
1994 f-250 idi turbo 330K
1986 f-350 IDI
1987 F-350 IDI

1985 JD 1050 4wd
1965 IH 3660