What Is the Snap-Action Mechanism in a 19mm SPDT Micro Switch?

The snap-action mechanism is a spring-loaded, precision-engineered component inside the 19mm SPDT micro switch (and most micro switches, including micro limit switches) that enables an instantaneous, non-linear state change when the switch is actuated. Unlike gradual-contact switches (e.g., some toggle switches), it relies on two key parts: a flexible contact arm (connected to the COM terminal) and a torsion or compression spring that stores mechanical energy during actuation.

When an external force (e.g., a lever, plunger, or button) presses the switch’s actuator, the spring compresses slowly at first—this is the "pre-travel" phase. Once the actuator reaches a critical threshold (the "trip point"), the spring releases its stored energy suddenly, snapping the contact arm from its resting position (connected to NC) to the activated position (connected to NO). This snap is mechanical, not dependent on the speed of the external force, ensuring consistent switching even if actuation is slow or uneven. In a 19mm SPDT micro switch, this mechanism is miniaturized to fit the compact 19mm housing without sacrificing precision.