The 2D drawing carries the numbers that decide whether the part assembles: thread size and length, mating depth, panel cutout diameter, hex flats, keyway position, and contact pitch. If the drawing shows only the outside profile, tolerance stack moves into email and becomes harder to control. A thread that is 0.3 mm long relative to the mating socket can interfere at assembly, and an overmold that extends past the panel cutout can require rework during installation. Put the cutout and mating envelope on the same sheet as the insert view so both sides work from one reference. Drawing approval then becomes a real decision tied to dimensions. The 3D model answers fit questions that a dimensioned sheet leaves open. Cable bend radius behind a 90° boot, wrench swing for the locking nut, connector-to-connector clearance on a crowded plate, and harness routing through a machine frame show up in the assembly model before tooling is cut. During new machine module prototyping, this is where interferences surface: the coupling nut may foul a frame rail while the part is still a file. Sending a 3D file with the RFQ also saves a mail cycle because the supplier can place the proposed body into your assembly. Prototype validation closes the loop. The sample is built to the approved drawing revision, mated with the counterpart the design actually uses, and checked for contact resistance, insertion feel, and locking behavior. EN 60512-1-1:2010 provides background on how contact resistance and mating performance are evaluated in industrial connectors; the sample build shows whether a specific custom part meets its drawing. IEC 61076-4-001:1996 provides background for the M12 screw-locking interface, and IEC 61076-4-101:2001/COR1:2003 provides background for the M8 interface family. Use that background during drawing review, then approve the custom part through its drawing revision and sample results.