Threads and gears

Over-pin (over-ball) measurementOver-pin / over-ball measurement

Also called: over-pin method, ball-type tooth thickness micrometer, between-pin measurement (internal gears), single over-pin method

≡Standards, measuring range and accuracy

Standard: Not confirmed in public sourcesNo standalone standard was found
Measuring range: —Not confirmed in public sources
Resolution / graduation: —Not confirmed in public sources
Accuracy (instrument error / maximum permissible error): —Not confirmed in public sources

▦Types

Put 2 pins into tooth spaces at opposite ends of the diameter and measure over them (M_dR) / use balls (M_dK)

^[1][2]

Single over-pin method (distance M_rK from the contact in the tooth space to the gear center, used when there is no tooth space on the opposite side)

^[1]1 source, for reference

Ball tooth micrometer (for over-pin diameters). V-anvil micrometers are for tools with 3 or 5 flutes

^[3]1 source, for reference

◎Part names and functions

#	Name	English	Function
1	Pins (balls) / micrometer	Pins / balls	^[1][2]

◷How to read the scale

Even number of teeth: M = z·m·cosα/cosφ + dp; odd number of teeth: M = (z·m·cosα/cosφ)·cos(90°/z) + dp. φ is found from invφ = dp/(z·m·cosα) − (π/(2z) − invα) + 2x·tanα/z^[2][4][3]
Example (Kyoiku): m = 2, α = 20°, z = 30, x = 0.15, dp = 3.5 → M = 65.48 mm. Same conditions with z = 29 (odd) → M = 63.39 mm^[4]

✋Usage steps

Place pins (balls) in tooth spaces near opposite ends of the diameter and measure over them with the micrometer^[1]
For an odd number of teeth the opposite side is not a tooth space, so use the odd-tooth formula^[2][4][3]

Printed from Kezuriba (kezuriba.net/en/gauges/over-pin-measurement/)

✓Care, storage, inspection and calibration

Care and storage

Inspection and calibration

The three-wire method for threads uses the same idea (Mitutoyo E11003). The overpin_* formulas and examples in the gear DB can be shared.

⇄Related instruments

Gear tooth micrometer Outside micrometer Over-pin dimension calculation

📚Sources

Content without a mark is what agreed across two or more sources from different publishers. Procedures and cautions are summarized in Kezuriba's own words based on the sources, and the diagrams were drawn by Kezuriba. Accuracy values are manufacturers' published figures, not values from JIS tables.