Little bit of technical question regarding a decat.

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I have a 94' M reg, UK, 2 ltr.

The car has the a stainless backbox on it.

Now i've noticed that the flange on the cat is starting to rot so its time for a decat i think.

My fathers a machinist and has stainless materials to hand in work so im asking him to make it for me.

Problem is i need to give him some dimensions to work by.

I need to know what the wall thickness is of the tubing, thickness of the flange and the diameter of the tube.

Ive read for my engine that its the 420mm length pipe needed.

Any drawn plans online available would be great.

Any help will be massively appreciated!

thanks guys!