Mossberg 500, 500A, 500AT 590 12 Gauge Breech Bolt Assembly. Please know the part that you need and if it will work for your application. Due to the numerous variations in the gun parts world we will not accept returns due to ordering the wrong part, changed mind or it does not work in my application. We are not responsible for a part that that has minor or major differences from the variation of your model firearm, if in doubt it is better that you do not purchase the part.