Measuring ToolsMeasuring instrument
Thread Pitch Gauge
A fan of toothed leaves, each cut to one pitch, offered up to a thread until the teeth sit down into the flanks. Tells you the pitch without arithmetic.
What it does
- Naming the pitch of an unknown thread
- Separating a coarse thread from a fine one of the same diameter
- Checking a thread against a stated designation
What to look forthe judgement calls, before the spec sheet
- Metric gauges are marked in pitch in millimetres, unified gauges in threads per inch. They are not interchangeable and mixing the sets produces a plausible-looking wrong answer.
- A gauge that seats down into the flanks over the full length of the leaf is a match. One that rocks on the crests is not.
Misuse and safetythe ways this tool causes rework
- It identifies pitch, not diameter. You still need a caliper for the outside diameter, and the pair of readings is what names the thread.
- On a worn thread even the right leaf will rock. On damaged or rolled threads, measure over several turns and take the reading from the undamaged length.
Projects that call for itand what it is doing on each one
All projectsFrequently asked questions
How do I tell M8 from M8 fine?
By pitch: 1.25 mm for the coarse series, 1 mm for the fine one. The pitch gauge seats on one and rocks on the other, and the outer diameter is 8 mm in both cases.
Can I measure pitch with a caliper?
For a metric thread, yes — crest to crest over as many pitches as you can reach, divided by the number of spaces. It is less reliable than a gauge on short or damaged threads.