Explain the job before choosing the shape
Start with one sentence describing what the part must do. Add photos of the surrounding assembly, a sketch with dimensions and any existing files. Mark the surfaces that touch other components and identify where there must be clearance.
Label measurements with units and distinguish a measured value from an estimate. If a dimension is still unknown, say how it could be checked. That makes it possible to discuss a prototype for the uncertain interface instead of quietly building the estimate into the design.
Say what would make the first print successful
Choose the decision the first prototype must support: confirming a fit, comparing two forms, checking access or trying an interaction. Include the quantity, your timing and a rough budget so the design effort can be matched to that stage.
For functional requirements, describe the loads, environment and expected use as far as you know them. Flag any required ratings, reports or approval process at the start. We can then agree what the quote includes before design or printing begins.
Questions about prepare your design brief
Can I enquire without an STL or CAD file?
Yes. Send a sketch and photos, with any measurements you can take. The enquiry can include model development as a separately quoted part of the work.
Which file should I send if I already have a model?
Send the original editable model or STEP if available, plus a mesh such as STL or 3MF if that is what you have. State the units and identify the current version so we can review the correct geometry.