These flats are made from 4130 annealed steel as well as the rails.
This is an image of the new Polish Underfolder flat that I'm having made from scratch. Each flat will come with a set of rails with mag stabilizers on each side. These are stamped from raw materials and are NOT modified flats from any other manufacturer.
This flat will not work with the Yugo M70, Yugo M92, Hungarian AMMS or Romanian underfolder rear trunnion.
To finish these flats along with the others you will need to buy a 5mm and 7mm reamer. Or at least get drill bits of that size to open up the holes in the flats once they are bent. The reamers should cost around $27 for the set plus shipping from most online tool suppliers. At the same time you order the reamers buy 4mm (or 5/32) screw machine drill bits for drilling the trunnion holes. The rear trunnion holes are 4.5mm. Try not to buy the cheap import drill bits for drilling the trunnion holes.