Here is what Mr. Curtis says.
To use these flats you will need to have a 5mm and 7mm reamer. This will help solve two of the problems with the flats currently on the market. In all there are at least five problems that will be fixed with these flats compared to any offered before.The rails that will come with the flats are pictured below. They have mag stabilizers on both rails to keep the mag from tilting and causing feed problems. The picture of the rails are from the actual samples and are made from 4130 steel. Yes, I had samples made and tested them before shipping any flats. I bet no other company that sells flats ever went to that much trouble. These were designed from an actual receiver from Romania then during the later runs of rails I switched to the longer length rail like the Bulgarians used.