Find a scrap or cut off a piece of aluminum bar stock 2 or more inches in length, roughly 1 inch in diameter, then find a standard imperial Vernier (not dial, metric, or digital). Bring it to the instructor. Indicate the current dimension as you understand it, then have the instructor confirm that it is correct. Then the instructor will give you a size to stamp on the bar stock.

If unfamiliar with lathe operation see HERE

Chuck the material (no, that doesn't mean 'throw it') insuring the key is removed, end face and center drill. Turn approx. 1 inch to the given dimension (Hint in order to avoid going under size only remove 1/8 in length then stop the machine and check before continuing to cut the full 1”, but try not to move the cross-feed crank so that the toolbit tip remains at the same depth.)

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A level 4 is within 002”

A level 3 is within 005”

A level 2 is 010” or more