Welcome to ak-builder.com!
Finally there is an alternative to the home builder to make your own professional grade 1.5mm receiver from a flat. The material these are made from is .063 4130 Chromoly steel that is in the annealed condition. Yes annealed means it needs to be heat treated. Yes the flats come with rails as always and both are made from annealed 4130 and are .050" thick. The mag stabilizers/guides need to be trimmed just like all of my other rails. There are no front trunnion holes drilled and the hammer, trigger and center support holes need to be drilled also. This is to allow you to make the receiver like it should be done to be as perfect as possible. Holes that are too close to a bend will stretch which is bad for the trigger pin holes.
This item is made in the United States and counts as a 922r compliant part.