Strike Industries specifically states: "Will not properly fit with Aero Precision M4E1 upper receivers"
This cover fits Aero Precision M4E1 Threaded upper perfectly. I bought the FDE one without reading this Q/A. Good thing I didn't read it as it fits my Aero Precision M4E1 Threaded FDE Upper perfectly. The FDE color is a little lighter than the upper's FDE color but still a good match color wise. I wish I could post a photo to show you.
There may have been some recent changes by Aero Precision or Strike Industries. I just tried one of these covers in two different, recently purchased M4E1 uppers. in the anodized upper, it functioned perfectly. In my cerakoted upper, it still functions as it should but pivots a bit stiffly, most likely because of the cerakote.
I have one on my m4e1 upper fit with no issues
This fit on 2 out of my 3 Aero M4E1 uppers. I have 2 dust covers and they both fit on 2 of the uppers. The other upper would not accept either dust cover.