Thread pitch counter
Hold the screw against a ruler, count how many thread crests fall inside the span, and type that number in.
Span measured
Pitch
0.50 mm per thread
Closest metric sizes
- M3 standard pitch 0.50 mm — strong match
- M4 fine pitch 0.50 mm — strong match
- M5 fine pitch 0.50 mm — strong match
Nearest US thread: #2-56 UNC at 0.45 mm pitch, 2.18 mm across. If your diameter matches that better than the metric options, you have an imperial screw.
Pitch alone is not enough
Several sizes share a pitch, so measure the diameter as well. Pitch is what tells you whether a screw of the right diameter is fine-thread or a US size in disguise.
Measure the diameter too →Gear for this job
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Thread pitch gauge (metric + imperial)
Reads the pitch in seconds
Digital caliper
Measure diameter and length properly