There are a lot of adapters to make your standard AR Lower fire 9mm. If you do not use a 9mm buffer with the new AR9 setup, you will destroy some parts in the lower. This plug adds the length of an 9mm buffer to your standard AR buffer. This plug is two pieces so you can add an individual buffer weight inside and then screw the cap on to retain the weight. Print with a wall count of 15 and infill of 100%.