🔍 Key Concepts

• Match each label (A, B, C, D) to common machine-shop hole types: countersunk, counterbored, counterdrilled, spot-faced. • Focus on the shape of the top enlargement of each hole (conical vs. cylindrical, deep vs. shallow). • Remember that some operations are meant to seat a fastener head (like a bolt or screw) and others just clean/flatten a surface.

💭 Think About

• Look closely at hole C: is its upper enlargement deep or shallow compared to B and D, and does it look like it is meant to fully recess a bolt head or just alter the entry of the hole? • Which type of hole is typically used to create a flat bearing surface on a rough casting, and which is simply a second drilling operation with a larger diameter? • Compare C to B: both are cylindrical enlargements. What subtle difference in depth and purpose would distinguish a counterbore from a counterdrill or a spotface?

✅ Before You Answer

• Identify which illustration clearly shows a conical mouth (that one is the countersunk hole; eliminate that choice for C). • Decide which one shows a deep cylindrical recess with a flat bottom sized for a bolt head (that one is the counterbore; eliminate that choice for C). • Between the remaining two terms, ask: which one describes a shallow surface-cleaning flat around the hole vs. which one describes a step-drilled, larger-diameter section of the same hole? Match that idea to what you see at C.