These Pro series studs from ARP are cold-forged to ensure molecular integrity. They are heat-treated prior to thread rolling and machining and are rated at a whopping 190,000 psi. The Pro series kits are also available with 12-point nuts, and all kits come complete with hardened parallel washers for an even load distribution and accurate torque readings. These Pro series studs from ARP are cold-forged to ensure molecular integrity. They are heat-treated prior to thread rolling and machining and are rated at a whopping 190,000 psi. The Pro series kits are also available with 12-point nuts, and all kits come complete with hardened parallel washers for an even load distribution and accurate torque readings.