🔍 Key Concepts

• Tap drill size vs. tap (thread) diameter and how threads are formed • Difference between major diameter and minor diameter of a thread • Purpose of drilling before tapping (material for thread teeth vs. clearance)

💭 Think About

• Think about what happens physically when you cut threads with a tap—where does the metal for the thread form come from? • If the hole were exactly the same size as the tap, would the cutting edges of the tap actually remove metal to form threads, or just rub? • Consider what would happen if the drilled hole were too big or too small—how would that affect how well the bolt fits and the strength of the threads?

✅ Before You Answer

• Remember that a tap cuts threads into solid material left in the hole wall, so the drill size must leave enough metal for thread depth. • Distinguish between the tap’s outside (major) diameter and the smaller core (minor) diameter that corresponds more closely to the drill size. • Ask yourself: for a standard tapped hole, is the drill sized to the tap’s major diameter, minor diameter, or something else?