When you want your build to look as original as possible the first thing everyone notices is the mag-well dimples. Mag-well dimples are a dual purpose feature that stabilize the magazine to keep it from wobbling and as an added benefit also strengthen walls of the receiver. They look great and every country uses a different style embossment to form the metal. AK enthusiasts with a well trained eye can quickly differentiate receivers by sight from this feature alone.
The drawing above is showing that the proper distance between the lower stabilizer rails for a 7.62x39 receiver @ 26 mm. The .5 mm dimension is the minimum thickness of the metal for the mag-well dimples after the stretching from forming and the milling to size has taken place. In actual practice the stretching of the metal happens more on the sides of embossment than the bottom. This works out nicely because the you are then left with a larger contact patch to mill and get a better magazine fit with less wobble. On Bulgarian and Russian 5.45x39 receivers the dimple is much deeper and the bottom stabilizer rails are also extended. This allows a tight fit on the thinner magazines.
The hardened and welded receiver blanks as well as the fully finished receivers both are correctly sized after the spot welding of the bolt guide rails. This is great added benefit to customers because you now are purchasing receiver blanks that have been pre sized for a perfect fit and look beautiful.