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.
Rise Armament, Anti-Walk Trigger & Hammer Pins, AR15 & AR10 Compatible
AR Triggers & Anti-Rotation Trigger Pins - School of the American Rifle - AR Build Junkie
PIN SET, AR PLATFORM, HAMMER/TRIGGER, ANTI-WALK, STAINLESS
KNS Anti-Walk Hammer Trigger Pin Gen ST Non Rotating AR-15, LR-308
Rise Armament Anti Walk Pins
Strike Industries Anti-walk/Anti-rotation Trigger/Hammer Pins
AR-15 Complete Anti-Rotation Trigger/Hammer Pin Set (Anodized Black) » Guntec USA
AR 15 Complete Lower Parts Kit 1pk 38-Piece - Nickel Boron + Extras
AR-15 Complete Anti-Rotation Trigger/Hammer Pin Set (Anodized Black) » Guntec USA
Trigger Upgrade Kit Trigger + LPK + Grip + Anti Walk Pins