This is a Apex Tactical Specialties Trigger known as the S&W Shield Carry Kit, model SCK.
The Apex Duty/Carry Kit for the M&P Shield (9/40 only) was designed to provide a smooth" consistent trigger pull that is approximately 2 lbs. lighter (based on variations in factory tolerances) with the advantages of shorter over-travel and more detectable trigger reset.
Features:
Reduces trigger pull by approximately 2 lbs.
Smooth uptake and reset
Reduces over-travel and reset length
