Leave at least 1.5× pitch of relief at the bottom of a blind hole. Write three things on the drawing: thread spec, tap-drill diameter, and effective thread depth. For small threads and deep holes, do not write only “tap to the bottom.”
Relief is the pitch on the drawing times 1.5. If the designation and the pitch are not written, that length cannot be calculated. Coarse threads are more general. They tolerate dirt and assemble more easily. Fine threads are for thin walls, adjustment, or a shorter engagement. After the thread form is chosen, relief is still left to that pitch.
Tapping or thread forming follows the drawing. Critical threads must be called out. Drilled and milled holes follow the reach of the tool. If the threads still get anodize or powder coat, mating threads are masked by default. After coating, threads seize.
Write the thread spec, tap drill, effective depth, and bottom relief into the PDF. Upload the STEP, select the thread tier in the quote, and see the itemized reference price. Where the note only says “tap to the bottom,” that feature is not fully quoted until engineering confirms it. A reference price is not a contract.