A hole designed to seat a rivet or bolt head flush with or below the surface is called which?

• A. Countersunk hole
• B. Pilot hole
• C. Clearance hole
• D. Datum hole

Answer: (A)

A countersunk hole is used when you want the head of a rivet or flat-headed bolt to sit flush with or below the surrounding surface. It’s shaped as a conical recess so the head can sit down into the material without sticking out. The screw or rivet head matches the angle of the countersink, so the top surface remains smooth and level.

This differs from a pilot hole, which is just a starter hole used to guide drilling and doesn’t create any seating for a head. A clearance hole is sized to let a bolt pass through without threading into the opposite part, so it won’t seat a head in a recess. A datum hole isn’t for seating a fastener at all; it’s used as a reference point for measurements and alignment.