Gear Over Pins
Find the best measuring pin size first, then calculate the theoretical measurement over the pins you actually have.
Recommended Measuring Pins
Choose the closest pin you have. The best size places theoretical flank contact at the reference circle.
Use the Pin You Have
Enter the exact diameter of the gauge pin you will put in the gear. The theoretical over-pins measurement will be calculated for that pin.
Measurement Over Pins
Theoretical nominal measurement for the exact pin diameter entered above.
How to Measure
The drawing uses the calculated gear tooth count and involute tooth form. Seat equal pins in the indicated tooth spaces and measure across their outside surfaces.
Calculation Rules & Open Sources
The pin calculation uses standard involute spur-gear geometry. For the recommended pin, the pin is chosen so its theoretical involute contact point is at the reference circle. For an entered pin diameter, the tool solves the inverse involute function and applies the separate even- and odd-tooth over-pins relations. The minimum and maximum pin diameters are geometry limits for theoretical contact to remain on the active involute, from its start through the outside diameter. They are selection limits, not drawing acceptance tolerances.
The mathematics is independently implemented and regression-tested against open-source gear references, including Cogwright (GPL-3.0) and the existing FreeCAD/BOSL2 geometry references. No proprietary pin tables are embedded in production.