Skeletonized aluminum jig lets you observe the function of the sear, hammer, and disconnector engagement points while under normal spring tension. Jig interior is machined to the exact dimensions of the AR-15 fire control pocket. Open sides of jig offer plenty of room to make adjusts to the trigger assembly without having to take it in and out of the rifle. Jig can be mounted in a vise or on a pistol grip. Plastic block permits dry firing the assembly and won’t damage the hammer or jig.