B2X4/2X4 ARP Primo HSK

B2X4/2X4 ARP Primo HSKNo longer is it necessary to order the Ford Pinto head studs kit and also buy the appropriate washer separate. This kit is assembled from individual ARP parts and includes the appropriate washers. This kit also features ARP 6 point (hex) nuts instead of the typical 12 point nuts. Its been long established that ARP fasteners require re torqueing on a regular basis. In our experience, this could be due to the 12 point fasteners having very little

  No longer is it necessary to order the Ford Pinto head studs kit and also buy the appropriate washer separate. 

  This kit is assembled from individual ARP parts and includes the appropriate washers. This kit also features ARP 6-point (hex) nuts instead of the typical 12-point nuts.
  Its been long established that ARP fasteners require re-torqueing on a regular basis. In our experience, this could be due to the 12-point fasteners having very little material. The 6-point nuts have must more material to them and are less prone to thermal expansion, providing superior torque retention.

 U/C (Undercut) vs Standard shank studs
  Undercutting of the stud equalizes the "stretch", which makes for a more consistent clamping force; and one that compensates for head gasket compression when the cylinder heads are installed. This helps prevent blown head gaskets, and assures optimum engine sealing.

  All ARP's Head Studs are thread rolled after the heat treating process, which vastly improves their fatigue tolerance. These kits are manufactured from premium 8740 chrome moly steel and heat treated to 190,000 psi. Alternatively ARP2000 series studs are available which are heat treated and able to withstand 220000 psi.

What is the difference between 8740 Chrome Moly and ARP2000?