It is the practice in shrunk fits to allow 1/1000 of an inch for each inch in diameter.

To illustrate: A locomotive tire 68 in. in diameter should be turned 68 X 1/1000 in., or 68/1000in., smaller than 68 in. Expressed in a formula this is:

A = .001 X D = D /1000 in. Where A is allowance in inches, and D is diameter in inches.