When sourcing CNC parts, you must provide a detailed Technical Data Package (TDP). This includes 2D drawings (PDF/DWG) with tolerance callouts and 3D models (STEP/IGES). Key specifications include material grade (e.g., Aluminum 6061-T6, Stainless Steel 304/316), dimensional tolerances (standard is +/- 0.1mm, but precision parts may require +/- 0.005mm), and surface roughness (Ra) requirements. Clearly define surface treatments such as anodizing, bead blasting, or electroplating to ensure the final product meets functional and aesthetic needs.