Hole features — naming the conical recess What is the correct term for a conical-shaped recess around a hole, most often used to seat a flat or oval head (tapered) screw flush with a surface?

Introduction / Context:
Mechanical drawings specify hole features to accommodate different fastener head forms and functional needs. Correctly distinguishing between counterbore, countersink, spotface, and boss ensures that the part is machined and assembled as intended.

Given Data / Assumptions:

• The recess is conical in shape.
• It is used to receive a tapered screw head so that it sits flush or slightly below the surface.
• Standard drafting and machining terminology is used.

Concept / Approach:
A countersink is a conical recess, typically at standard included angles (for example, 82 degrees or 90 degrees depending on regional standards). A counterbore is a cylindrical, flat-bottom enlargement for socket head cap screws. A spotface lightly faces a small circular area to create a flat seating surface. A boss is a protruding cylindrical feature, not a recess.

Step-by-Step Solution:

Verification / Alternative check:
Compare standard hole callouts: “Ø6 CSK 82° for flat head screw” denotes countersink; “Ø6 C’BORE Ø10 x 5 deep” denotes counterbore—clearly different geometries and tools.

Why Other Options Are Wrong:

• Boss: protrusion, not a recess.
• Spotface: shallow facing for flatness, not conical.
• Counterbore: cylindrical enlargement with flat bottom.

Common Pitfalls:

• Specifying the wrong angle for the fastener standard, leading to poor seating or damage.
• Confusing countersink symbols with counterbore symbols in CAD annotations.

Final Answer:
Countersink