Sadly, no sarcasm. While there are (very old and strangely named) standards in the US for the threads themselves, there aren't any for thing that have those threads.
So you could have one manufacturer who makes thicker walls to increase strength, one who makes really thin wall to cut their material costs, one who has sloppy machines and products with loose tolerances, etc.
And that's not even getting to different materials....
What was the topic again? (there's yer sarcasm!
)