When sourcing CNC turned parts for automotive assemblies, the tolerance callout is where most supplier disputes start. Leaving a bushing diameter at ±0.1 mm gets you a part that looks right on the bench and binds inside the housing.
Tolerance Risk in Automotive Precision Components
For a brass sleeve or stainless steel pin going into a sensor housing, the critical dimension is usually the outside diameter and bore. If the drawing says ±0.05 mm but the part must slide freely in a polymer overmold, state the fit class or go/no-go gauge explicitly. A thread on a copper insert nut adds another layer limits: specify the thread gauge class (2A or 3A) and engagement length. Skip that and the shop defaults to 2A, which may not clear your housing.
Weeda Precision sees RFQs where the drawing is still on the initial print revision but the part has already been reworked twice in production. Tying the drawing number and revision to the RFQ, plus stating whether the order is prototype, batch, or annual run, keeps the quote aligned with the actual need.
Material and Inspection for Automotive Precision Components
Material choice changes the inspection story. Brass C36000 is common for threaded inserts because it machines fast and threads cleanly. Under-the-hood applications push you toward bronze or stainless 316, and the tolerance budget shifts. Request a mill certificate and state whether a dimensional report or first-article inspection report ships with the lot.
Surface finish is a line item buyers often skip. A machined brass pin at 1.6 µm Ra looks fine under good lighting but will show scoring marks in a tight bore. Call the finish on the drawing or in the RFQ notes; "as machined" is not a specification.
What to Specify on Automotive Precision Components
A practical RFQ lists: 2D or 3D drawing with critical dimensions flagged, material grade, quantity split (50 prototypes, 2 000 pilot, 15 000 annual), target unit price at each tier, packaging requirement (individually bagged, VCI wrap, or bulk with separators), and the inspection method you will accept. For a knurled brass insert, add the knurl pattern and depth to the drawing notes so the CNC turning setup is unambiguous.
Before you release the RFQ, walk the drawing with your process engineer and mark every dimension that will be measured on the receiving bench. That single step cuts rework rounds more than any supplier conversation will.