When reasonable, which hole type should be used?

• A. Through holes
• B. Blind holes
• C. Counterbored holes
• D. Tapped holes

Answer: (A)

When a hole must pass completely through a part, a through hole is the simplest and most economical choice. It allows bolts, pins, or shafts to go all the way through and lets you access the other side for a nut or mating feature, which also makes alignment and assembly easier. Drilling a through hole avoids the depth-control challenges and additional operations associated with stopping at a specific depth, so it’s quicker to manufacture and typically cheaper while still meeting functional requirements.

If you only need a hole to stop inside the part without passing through, a blind hole would be used. If you need to recess the head of a fastener so the surface stays flush, you’d choose a counterbored hole. If you need threads inside the hole, you’d use a tapped hole rather than a simple through hole.