The Apex Duty/Carry Kit for the M&P Shield was designed to provide the Shield pistol owner 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. All of the components work together to provide a pull weight within the acceptable range for a top-end service pistol. However armorer or gunsmith installation of the Ultimate Striker Block (USB) into the Shield slide is strongly recommended. This kit includes 2-Dot fully machined sear Ultimate Striker Block Striker block spring Talon tactical tool Sear spring Slave pin and Trigger return spring.