Which drill size would you use to machine...

🔍 Key Concepts

• Tap drill size is usually slightly smaller than the thread’s minor diameter so the tap can cut the threads • For Unified / National Coarse (NC) threads, a common quick estimate for tap drill size is: tap drill diameter ≈ nominal diameter − 1 ÷ threads per inch • Compare each choice with the approximate diameter for a 3/4 inch, 10 TPI thread

💭 Think About

• First, estimate the tap drill diameter using the simple rule-of-thumb formula for tap drills and get a rough decimal value • Convert each fractional drill size in the choices to decimals and see which one is closest to your estimated tap drill size • Think about which options are obviously too small (would leave too much material) or too large (would leave almost no thread depth) for a 3/4-10 NC

✅ Before You Answer

• Confirm the nominal size is 3/4 inch and the thread pitch is 10 threads per inch (TPI) • Use the quick tap drill approximation: tap drill ≈ major diameter − 1/TPI and compute that value in inches • Double-check that your chosen drill size is smaller than 3/4 inch but still leaves enough material for proper thread depth

Which drill size would you use to machine and tap a 3/4 -10 National Coarse internal thread?

27/64 inches

31/64 inches

21/32 inches

25/32 inches