HF-601 is a collaboration between Hodge Defense Systems and Forward Controls Design. HF-601 is based on their PF-040 pins, with Jim’s input on what he wants on HDSI ARs. Like PF-040, they’re 17-4 stainless steel, precision billet machined on Swiss machines with high degrees of precision and very tight tolerances, and black nitride treated. HF-601 pins are 0.040″ longer than TDP take down and pivot pins, another feature shared with their PF-040.