Trigger Pin
The small cross pin the trigger pivots on inside the action or trigger housing. A wear and fitment point in any trigger group.
The trigger pin is the pivot that the trigger swings on inside its housing. It looks trivial, but its fit is part of how clean a trigger feels: a pin and hole worn loose let the trigger wobble, adding the slop and grittiness that show up as inconsistent trigger pull.
In a drop-in match trigger the pins are held to tight tolerance for exactly this reason. When a gunsmith fits or tunes a trigger, pin fit is one of the details that gets attention, because lateral play at the pivot is play the shooter feels at the finger.