⚙️ Gear Pitch / Mod
The tooth size standard for pinion and spur gears — Mod (metric) and Pitch (imperial) systems aren't interchangeable, so a pinion and spur must match.
What it actually does
Gear pitch describes the size of the gear teeth. Two gears only mesh properly if they share the same pitch, so it is the compatibility number you must match when buying a pinion or spur — tooth count sets the ratio, pitch decides whether they fit at all.
In practice
Common pitches in RC are 48DP and 32DP, with 32DP being coarser and stronger and 48DP finer and quieter. Metric module gears such as Mod 1 and Mod 0.8 are used on larger models. Finer pitch means more teeth engaged and smoother running; coarser pitch means stronger individual teeth.
Worth knowing
A 48DP pinion will appear to mesh with a 32DP spur and will destroy it quickly. If gears wear unusually fast or sound wrong, check the pitch matches before anything else.