ARP head studs for the 6.4L Powerstroke use premium grade 8740 alloy and a proprietary ARP2000 alloy that combine for a rating far superior to standard aircraft quality alloy steels. During manufacturing, each stud is placed vertically into special racks and precisely heat-treated to 200,000 psi for the 8740 material and 220,000 psi for the ARP2000 material. This ensures complete heat penetration and the results are far superior to those lesser quality studs from other manufacturers who just dump pieces into a basket and hope for the best.
Following the heat treatment, each stud is precision centerless ground to make sure it is as close to perfectly concentric as possible. This procedure involves about ten very slight cuts and results in an exceptionally straight part. It's important to note lesser quality studs are not even centerless ground. Instead they are often thread rolled in bar stock form. The tight tolerances and unparalleled precision that 6.4L Powerstroke ARP head studs are manufactured to, you will discover that gaskets and cylinder heads will glide right into perfect alignment - something that won't happen with inferior quality head studs.
ARP head studs for the 6.4L Ford Powerstroke are thread rolled after heat-treatment, which gives them 20-times better fatigue strength than inferior brands who thread their studs prior to heat-treating. It costs a lot more to do it this way, because it's tough on tooling, but the results are well worth the extra effort.