Certificate of Conformaty

[magicniner]

It's a thing which has come about with the rise of stockists and middle-men who don't make anything but miraculously sell products at many times the price of manufacture, as they have no clue about what goes into making what they're selling they have to have a piece of paper in the box with it which they can wave at their customers.
Large companies also have huge layers of bureaucracy and often require this kind of documentation for parts from outside suppliers.
There was a time when you quoted for a part based on a spec and delivered that part, at which point the customer would either accept or reject the product.
If the part is simply machined to their drawing your Certificate of Conformity could refer to the material cert and their drawing for spec with a note stating what process from the drawing is not to be carried out on the part by you, they will then be responsible for collating their drawing, the material cert you supplied and your CoC for downstream customers/compliance departments.

- Nick