Please answer my question.

What is the difference between the pipe machining and the fitting machining as below?

Why use "may be" and "shall be"?

- pipes

: A maximum of 1 mm (0.04 in) may be removed from each of the surfaces (i.e., internal

and external). Test specimen blanks shall not be flattened.

- fittings

: A maximum of 1 mm (0.04 in) shall be removed from each of the original surfaces. Test

specimen blanks shall not be flattened.