Backlash is the free rotation of the output shaft when the input reverses direction. 8 arcmin means roughly 8/60 of a degree of free play — about 2.3mm of wobble at the end of a 1m arm. Unacceptable for cobot joints.
Rule of thumb: pick-and-place tolerates 8–12 arcmin; welding and assembly want 3–5; precision machining and metrology demand ≤3 arcmin or a zero-backlash harmonic solution.
Three factors drive backlash: gear precision (ground vs hobbed teeth), carrier stiffness, and thermal expansion compensation under load. Cheap gearboxes that pass factory spec but double their backlash under load are common.
FJFilter's PLE series offers 8/5/3 arcmin tiers, 100% unit-tested with CMM reports, MOQ from 20 units.