Inner AEG barrels need to be modded ,and is a little tricky
,I screwed two inners before I got a system figured out.
The threads on the lower are totally different than most, for the stock tube,because they use a brass inner buffer tube and a M4 style outer that slides over.
The AEG outer barrels just need a small notch cut and a small hole drilled and taped for a set screw.
Hey Jeff,the inner and outer are held together with a small set screw,located on the top center, just in front of the flange on the outer barrel.
If you get an AEG outer for the KJ,make sure it's the deeper chambered one or the 1 cm adjustable one.Or
you can drill it deeper like I did,on one of mine.