HF-601 is a collaboration between Hodge Defense Systems and Forward Controls Design.
HF-601 is based on our 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 our PF-040.
Jim has a soft spot for Colt 601, thus HF-601 pins have taken on many of the Colt 601 pivot and take down pin cues. The dimples on both sides of the take down pin and left side of the pivot pin, even the slight ring on the left side of the take down pin tip is faithfully reproduced. The only exception is the pivot pin, whereas on the Colt 601, the right side pin head is flat, it is flat on the HF-601.
HF-601 can be purchased with the optional takedown/pivot detents (4) and springs (3) kit. The odd numbers of included components probably deserve some explanation. Even for experienced AR builders, it's not uncommon to launch the pivot pin detent into the twilight zone. It's also fairly easy to bend the take down pin detent spring during installation of the end plate and castle nut. So the optional detents and spring kit includes 4 detents and 3 springs to preempt losses and damages. If you don't end up needing and using all of them at once, the kit is reasonably priced, and always good to have on hand to grow into another AR :)
HF-601 pins diameter adheres to TDP dimensions and tolerances, 0.2485 +0.000/-0.005.