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. The external width of AR receivers varies in the trigger/hammer pin area, depending on the manufacturer. If the pins are too long for your receiver, you may shorten the pins a small amount by carefully filing material evenly from both ends of the pins. However, this is not required. Longer pins will not affect the function or performance of the rifle.