A __________ is best used for determining the number of threads per inch on a fastener.

• A. Caliper
• B. Micrometer
• C. Ruler
• D. Pitch gauge

Answer: (D)

Measuring how many threads fit in one inch means identifying the thread pitch directly. A pitch gauge is built for this task, offering a range of blades with different pitches that you compare against the fastener’s threads. When you find the blade whose threads match the fastener, you read off the pitch value, which corresponds to the number of threads per inch. This direct comparison is what makes a pitch gauge the best tool for determining TPI.

Calipers or micrometers measure overall dimensions like diameter or thickness, not how closely spaced the threads are. A ruler lacks the resolution to resolve thread spacing accurately, so it can’t reliably determine TPI. If you’re working with metric threads, you’d use a metric pitch gauge in the same way, but the principle remains matching the thread spacing to a reference pitch.