A hole in a 3D model is just a cylinder: it does not say whether it is threaded. So threads are declared separately when quoting and are not detected from geometry.
Threads
State whether the part has internal or external threads and detail them on the drawing:
- Full designation: M6×1.0, 1/4-20 UNC, etc.
- Thread depth when the hole is blind.
- Fit class if the application needs it.
Unless stated otherwise, threads are cut to class 6H/6g (metric) or 2B/2A (unified) and checked with go/no-go gauges.
Inserts and hardware
Select the inserts option if the part takes threaded, heat-set or press-fit inserts or any installed hardware. It is an extra operation after machining and affects price and lead time. Include the insert manufacturer part number.
In 3D printing
A printed part with threads or inserts goes to engineering review: the slicer cannot see them and the instant price would not include them.