How to brief a prototype so the first print fits
What to put in a design brief: the job the part does, the dimensions that matter, and how many revision rounds you actually need.
The useful brief is boring. It says what the part has to do, what it must not hit, and which dimension is the one that cannot be wrong.
A photo of a broken knob helps. A photo with a ruler in the frame helps more. A caliper note that says "shaft is 6.0 mm across the flats" helps most. If you only know the outside of the machine, say so. Guessing a hidden shaft is how a pretty knob fails on the first try.
Simple part, mechanical assembly, and product concept are three different amounts of drawing. A clip is not a five-part latch, and a latch is not a product. Each package includes a set number of revision rounds. Extra rounds are a line item because they are hours, not a feeling.
You can buy the STEP, STL, and 3MF and print them somewhere else. You can add one proof from the P2S. A small batch is the same file printed 5, 10, or 25 times, with the setup paid once. None of that starts until you accept the quote.