ARPFord 4 and 6-cylinder, 2.3L Duratec (2003 later), 12-point nuts, ARP Head Studs 151-4204ARP Head Stud Kits with 12-point Nuts. It is for good reason that virtually every top professional engine builder relies on ARP head studs for their all-out competition powerplants. Simply stated, theres not a better stud setup on the market today.For openers, ARP Head Stud Kits uses a premium grade 8740 alloy that is rated far superior to aircraft quality. Then, each stud is placed vertically in special racks and precisely heat-treated to 200,000 psi. This procedure ensures complete heat penetration and the results are far superior to those lesser quality studs from other manufacturers who just dump pieces in a basket and hope for the best.Following heat-treat, each ARP Head Stud is centerless ground to make it as close to perfectly concentric as possible. This procedure involves about ten very slight cuts and results in an exceptionally straight part. Its important to note that lesser quality studs are not even centerless ground the material is thread rolled in bar stock form (mostly before heat-treat, when the material is easier to machine).Because ARP Head Stud Kits are manufactured to such exacting tolerances, you will note that gaskets and cylinder heads literally glide into position and are perfectly aligned something that wont happen with inferior quality head studs.ARP Head Stud Kits are thread rolled after heat-treat, which gives them about 1000% (thats ten times) better fatigue strength than those studs that are threaded prior to heat-treat (a very common industry practice). It costs a lot more to do it this way, because its tough on tooling, but the results are well worth the extra effort.You will also note that ARP offers specially undercut studs for several engines. This procedure (done only to the shorter studs) more equalizes the stretch of both studs, which makes for a more consistent clamping force and one that compensates for hea
