These AR15 anti walk / anti rotation hammer and trigger pins are what you need to keep your receiver from excessive wear and tear. Keeping the hammer and trigger pins from rotating is especially important when shooting full auto or with pistol caliber builds, such as 9mm AR15's.
Strike Industries Anti-walk/Anti-rotation Trigger/Hammer Pins
Wilson Combat Anti-Walk Hammer/Trigger Pin Set, Black: MGW
KNS Anti-Walk Hammer Trigger Pin Gen ST Non Rotating AR-15, LR-308
WCA TRIGGER-HAMMER PINS ANTI WALK SCREW TYPE STAINLESS 0.154
AR 10 Trigger Pins For Sale
Rise Armament, Anti-Walk Trigger & Hammer Pins
James Madison Tactical Black Ops Evo Single Stage Trigger
Armaspec Anti-Walk Trigger / Hammer Pins Stainless .154 for ar-15
Trigger Upgrade Kit: Davidson Defense AR-15 3 lb Drop In Sierra